#help-10

1 messages · Page 565 of 1

misty terrace
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The \emph{general} construction of the center of the circle that is tangent to two given circles $\Gamma_1$ and $\Gamma_2$ (with centers $M_1$ and $M_2$ and radii $r_1$ and $r_2$ respectively) and a line $\ell$ where $\Gamma_1$ and $\Gamma_2$ are on the same side of $\ell$ that I found is pretty complicated, but bear with me:
\begin{enumerate}
\item Construct the line $k_1$ as the line on the other side of $\Gamma_1$ with $d(k_1, \ell) = r_1$ and $k_1 \parallel \ell$, and construct $k_2$ analogously.
\item Let $p_1$ be the parabola with focus $M_1$ and directrix $k_1$, and define $p_2$ analogously.
\item The intersection point of $p_1$ and $p_2$ is the desired center of the circle that is tangent to $\Gamma_1$, $\Gamma_2$ and $\ell$.
\end{enumerate}
This works since all points $P$ on $p_1$ suffice $d(P,\Gamma_1) = d(P,\ell)$ and similar. \\ \quad \\
In your case, however, $\Gamma_1$ and $\Gamma_2$ have the same radius $r$ and are of equal distance to $\ell$. In that case, there's nothing holding you back doing some Pythagoras and get the radius $R$ of the wanted circle, then getting the intersection of the circles with centers $M_1$ and $M_2$ with radius $r + R$. (Now that I think about it, the same might be possible for the general case as well... Let me think about that.)

https://cdn.discordapp.com/attachments/757583324632973403/937862098753568798/unknown.png

warm shaleBOT
misty terrace
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the 'you' here is not you

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wait maybe you can replicate the parabola construction

small kestrel
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well I mean it's a task in past finals of my geometry class and we didn't go over parabolas and hyperbolas yet, so i believe there should be another solution, but thank you very much for your contribution ❤️

misty terrace
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nah you just use the idea behind parabolas

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lemme see if i can turn this into a construction

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oh yeah you can

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nice!

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@small kestrel here is one of the circles!

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either you can ask what's going on or why it works or figure it out yourself based on this one picture alone :p

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the other is analogous

small kestrel
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hmm, i'll try to understand, but anyways i found an interesting property as well - it turns out the centerpoint is a vertex of a regular pentagon with one of the sides being O_a O_b

misty terrace
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by the power of a point (or just 'symmetry' lol) the midpoints of the circles that suffice must lie on the radical axis of the two circles, so by considering the two cases internally and externally tangent you see that there are only two options for the circles only

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that's surprising, woah

misty terrace
small kestrel
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shoot, so it was just a coincidence 😦

misty terrace
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let me give the explicit steps of the construction btw

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you can choose to prove the construction yourself if you wanna

small kestrel
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shoot

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didnt mean to include the pic

misty terrace
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  1. starting condition
small kestrel
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yup, that's basically the pic we start with

misty terrace
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  1. perpendicular bisector of the two midpoints of the circles
small kestrel
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that's where I ended KEK

misty terrace
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  1. circle with same radius of the two circles at the intersection point of the perpbis and line
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for externally tangent: draw a tangent line with the perpbis through the intersection point with the circle opposite from the two given circles

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wait that's not even needed

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nvm that

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  1. perpendicular bisector between intersection point and one of the given origins
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  1. result
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for externally tangent: take the intersection point at the same side of the two given circles

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thanks for the nice problem!

small kestrel
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ooh! thank you so much! i love you!!

misty terrace
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funny degenerate cases

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interesting how this all checks out in general form

small kestrel
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however, I just found out the teacher wants us to prove our constructions afterwards at our oral exam, would you mind explaining why this works?

misty terrace
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oh yeah ofc! it's very much based on the construction of some points on a parabola

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let me use some good letters for once

small kestrel
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of course, feel free to!

misty terrace
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basically, what you want to find for the first circle is the point E such that length EC is the same as the distances to w1 and w2

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so you want to find E such that EC = EB - r

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but that's the same as EC + r = EB

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so using the perpendicular bisector of BD, we find E such that ED = EB, so EC + r = EB

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which gives us exactly the point we need!

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you can see it like this: you want to find the isosceles triangle ECF but don't have E or F, but you do have enough information for the extended isosceles triangle EDB

small kestrel
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i seriously love

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you

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so

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much

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you just blew my mind

misty terrace
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<3

small kestrel
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it looks so simple and yet so challenging

misty terrace
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uh huh

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one of the reasons i like euclidean constructions

small kestrel
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do you study maths or is that just a hobby of yours?

misty terrace
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i'm only in high school :p

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so a hobby ig

small kestrel
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are you kidding me

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im at uni and wasn't able to do it

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well tbh, im so bad in geometry

misty terrace
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well, i do get invested in math a lot

small kestrel
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and i have to take three semesters of geometry, this is just the first one 🥲

misty terrace
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oof

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can't imagine the next ones

small kestrel
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well the next ones are more about calculating

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this one is about constructions

misty terrace
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i have mixed feelings about that

small kestrel
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geometry has always been my nemesis

misty terrace
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yeah people are very divided about their opinions on geo

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one of the trainers (at the dutch math training camp) said that there is some kind of 'click'

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between not liking geo and loving it

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guess i'm in my click phase

small kestrel
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i guess my click phase has yet to come

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i'm more into algebra, you know

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or combinatorics

misty terrace
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yeah i see

small kestrel
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or number theory, but I don't have as much knowledge about it

misty terrace
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i like combi but only when i see the proof

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i've only done elementary nt/alg/combi/geo though

small kestrel
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i'm taking the number theory course in like two years' time

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nt?

misty terrace
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number theory

small kestrel
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oh

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im dumb

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oops

misty terrace
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eh, you didn't know an abbreviation that isn't a reason to be dumb

small kestrel
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i also tried digging into game theory, it's such an interesting topic but quite challenging as well

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and one more question! what is the cool software you are using for constructions?

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the one you were sending pictures from

misty terrace
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ah that's actually a game about euclidean constructions

small kestrel
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EUCLIDEA

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YES

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I FOUND IT TODAY AFTER FORGETTING ABOUT IT

misty terrace
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it's the easiest way to assure your euclidean construction is actually a construction

small kestrel
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I found it for the first time about five years ago when i was in high school

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and stumbled upon it again today

misty terrace
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well, have fun replaying it!

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by the way, i think the construction is generalizable? for any two circles

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okay maybe not

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but well, at least the two circles don't have to intersect

small kestrel
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oh, that's interesting!

misty terrace
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such a circle does seem to exist

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oops

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i think of my next message while i'm typing it and i write the wrong term

misty terrace
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uh

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colors :D

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ok well yeah, you can prove existence by two parabolas intersecting

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but how to do it with straightedge and compass?

small kestrel
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dude, i'm glad to know how to construct a circle using a compass, don't start on me with parabolas

misty terrace
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oh yeah lemme clean up a bit

small kestrel
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the last time i saw them was two years ago when i ended high school

misty terrace
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parabolas are just a tool helping us get the actual euclidean construction here!

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i wouldn't have come up with the solution to the original problem if it weren't for parabolas

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at least this quickly

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if we just knew how to construct the perpendicular line through J we'd be done by our previous construction

small kestrel
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dude, i feel so dumb, the only thing i know about parabolas is that they are described by a relationship between two points (i hope it's not a hyperbola) such that x^2-y^2 is constant

misty terrace
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uh, x^2 - y^2 = c is a hyperbola sadly :(

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you can define a parabola by a focus point F and directrix d

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then a parabola is the set of all points (locus) such that it has the same distance to F as d

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(the directrix is a line and the focus is a point)

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if only we knew how to intersect two parabolas with each other given focus and directrix...

small kestrel
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oopsie

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well as you can see, I know nothing about these things KEK

misty terrace
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i google how to construct the intersection of two parabolas

small kestrel
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also - what do you call them in english? i mean circles, ellipses, parabolas and hyperbolas?

misty terrace
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but i get equalling two polynomials of degree 2 with each other

small kestrel
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in czech we call them "kuželosečky", basically "the things that you get by cutting a cone"

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no, no, i mean the group of those four, do they have a name as a group?

misty terrace
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ah

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conics

small kestrel
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great! that will be a simple term to remember, thanks!

misty terrace
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google doesn't find anything about intersecting two parabolas given focus and directrix..?

small kestrel
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oh, i have no idea, i'm trying to jot down the proof of the construction KEK

misty terrace
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ah, turns out this is one of the types of apollonius's problem

small kestrel
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i am allergic to that name

small kestrel
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HOLY MOTHER OF JESUS

misty terrace
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8 solutions in general

small kestrel
misty terrace
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orientated circles?

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that sounds

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awful?

small kestrel
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it is

misty terrace
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what is it though

small kestrel
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well it means that you add orientations to your circles KEK basically arrows pointing in a direction, the same goes with lines
the tangent objects have to agree with their orientations

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look at this

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this is a valid tangent line to the circle, right?

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this is a valid tangent ray to a cycle as well

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(a ray is an orientated line and a cycle is an orientated circle)

misty terrace
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hmm

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are there any nice properties about them?

small kestrel
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but this

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is not valid

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they dont touch KEK

misty terrace
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that feels so unnatural

small kestrel
misty terrace
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aw :(

small kestrel
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i can try tho KEK

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oh, okay, i can't

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i thought i found a dictionary that has those terms in it

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but it doesn't KEK

small kestrel
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it doesn't matter tho, i'm not that skilled a geometer to be able to explain it even in czech, i think KEK

misty terrace
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ah ok that's fine :p

small kestrel
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so i think i'll just close this thread as we don't talk about the topic anymore so that somebody else can use it

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.close

obtuse pebbleBOT
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quaint tangle
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i keep getting 3 or 10 and i was wondering if anyone could walk me through this problem

timid silo
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can you just clarify what the o denotes

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haven't dealt with that notation for a long time

quaint tangle
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its basically g(f(x))

small kestrel
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oh, sure, you just take the 2 as the argument of f(x)

quaint tangle
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at least that is my understanding

small kestrel
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and then you take this result as the argument of g(x)

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so you get g(f(2))

timid silo
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what a weird notation, why not just write g ( f ( 2 ) ), what's wrong with these conventions

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sorry just ranting here

small kestrel
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then, when you put the 2 into the f function, you get $g(\frac{2+3}{2})$

warm shaleBOT
#

Smethisko

small kestrel
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then, that is just $g(\frac{5}{2})$

warm shaleBOT
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Smethisko

small kestrel
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and as g(x) = x^2-1

royal shard
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it is actually a quite common notation

small kestrel
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you will plug in the $\frac{5}{2}$ to get $(\frac{5}{2})^2-1=\frac{25}{4}-1=\frac{21}{4}$

warm shaleBOT
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Smethisko

timid silo
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no thanks I hate that notation

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but yeah what the others said is right

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you just do f

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and then g

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with what you get from f

hexed agate
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Ever wondered why f and g were chosen as the letters?

small kestrel
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i mean when you have 3 and more functions, the f(g(h(x))) just gets confusing

timid silo
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as a hobby programer I disagree

small kestrel
timid silo
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I like my brackets

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because mathematicians are fagg*ts ?

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can I say that here?

small kestrel
hexed agate
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Mathematicians love to fuck

fringe minnow
cedar lichen
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ice people :)

devout solar
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No

fringe minnow
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friendly reminder, this isnt #general

hexed agate
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Says the one finding a gf

quaint tangle
#

.close

obtuse pebbleBOT
#
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cedar lichen
obtuse pebbleBOT
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glass parrot
#

isith thy correct

obtuse pebbleBOT
cedar lichen
#

Yes

timid silo
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ye

fringe minnow
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yes

glass parrot
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yes

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.close

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little jacinth
#

hiya, could someone help me workout this problem?

timid silo
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how would you approach this?

little jacinth
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one sec, sending my work

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ok there it is

timid silo
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ok so the first thing I'd do

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is complain to your teacher

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for using this notation

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a^6 : a^4 -6a

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is ambiguous

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does the 6a belong in the numerator

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or denominator?

little jacinth
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lmao its a practice test for an exam i have coming up

little jacinth
timid silo
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based on the given answers

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I would say it's supposed to be

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(a^6 / a^4) - 6a

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but notation like that

little jacinth
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my guess is the a^4-6a is denominator

timid silo
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drives me up the wall

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since there's 3 ways of interpreting that

little jacinth
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yeaaah im not exactly a fan either trust me

timid silo
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ok so in the first part

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we just add up and subtract the exponents

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to get -a

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and that squared gives a^2

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right?

little jacinth
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right

timid silo
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and for the second part

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assuming my notation

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it would be 5 * ( a^2 - 6a )

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so thats 5 a^2 - 30 a

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  • that one a^2
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gives 6 a^2 - 30 a

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we factor out 6a

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and get

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6a * (a - 5)

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which is the correct answer

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so yeah, you missinterpreted the notation

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because that notation should burn in hell

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not your fault though, I don't blame you at all for making that mistake

little jacinth
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thank you so much

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its miles more clear now

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ngl the notation made me really unsure on how to interpret this

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and it turned into a hot mess

hexed agate
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To be devil's advocate, there is a clear difference between a^6:a^4 -6a and a^6:(a^4-6a)

timid silo
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with brackets it's fine

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clear

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well defined

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without brackets

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it's an abomination

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a terror among fiends

solar trellis
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$\int_{\partial S} \bf{F}\cdot \dd{\bf{r}} = \iint_{S} \nabla\cross\bf{F} \cdot \dd{\bf{S}}$

warm shaleBOT
#

giannis_money

timid silo
#

don't get me started on nabla

hexed agate
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What is nabla?

solar trellis
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what's wrong with nabla

timid silo
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(resisting urge to say nablabals)

solar trellis
little jacinth
#

.close

obtuse pebbleBOT
#
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obtuse pebbleBOT
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timid silo
#

The table below gives the literacy rate (in percent) of 30 cities surveyed. What is the lower limit of the median class, the median of the data, and the mode of the data?

timid silo
obtuse pebbleBOT
#

@timid silo Has your question been resolved?

timid silo
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<@&286206848099549185>

obtuse pebbleBOT
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@timid silo Has your question been resolved?

timid silo
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<@&286206848099549185>

timid silo
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<@&286206848099549185>

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vernal knoll
#

I’ve eliminated the 4th option but I’m unsure still

vernal knoll
#

. Close

#

.close

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dense rune
obtuse pebbleBOT
dense rune
#

Somebody please help me solve for R

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What do i do wi th all those exponents

obtuse pebbleBOT
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@dense rune Has your question been resolved?

dense rune
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<@&286206848099549185>

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tacit mist
#

I need help with the following problem for real analysis:

Give a proof of the composition of continuous functions using the sequential characterization
of continuity (from Abbot's real analysis).

My idea is to show that since f is continuous at c, and g of f is continuous at f of c, we have a sequence xn that shows continuity f(xn) converging to f(c) and likewise g(yn) converging to g(f(c)). I'm not sure where to go from there though.

gilded needle
#

i think you mean "and g is continuous at f of c"

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suppose x_n is any sequence that converges to c, then by continuity of f, you know that f(x_n) converges to f(c)

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now what can you say about g(f(x_n))?

obtuse pebbleBOT
#

@tacit mist Has your question been resolved?

tacit mist
gilded needle
#

yes

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that's pretty much all there is to it

tacit mist
#

wait is that it?

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wow, thank you!

gilded needle
#

yep

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timid silo
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zinc escarp
obtuse pebbleBOT
zinc escarp
#

i just couldn't differentiate the given formula

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weak torrent
#

I am a bit confused with this question, Is it Row Echelon Form(REF) or Reduced Row Echelon Form(RREF)

weak torrent
gilded needle
#

row 1's pivot is to the right of row 4's pivot, that's not allowed in row echelon form

weak torrent
#

thanks man

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hidden bronze
obtuse pebbleBOT
hidden bronze
#

a) i got the zscore of klare which is 0.83

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b) and of simons which is 1

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why is C answer as: klare

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shouldnt it be simon

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<@&286206848099549185>

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can someone explain why

novel knoll
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ambigious what they mean with better time in comparison

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but yes Simon higher z-score

hidden bronze
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so

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is the textbook wrong

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or is it just weird they asked for a comparrision

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and if so, how would i calcualte which has better time in comparison

obtuse pebbleBOT
#

@hidden bronze Has your question been resolved?

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static sun
#

8!-7!

obtuse pebbleBOT
#

Please don't occupy multiple help channels.

static sun
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.close

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cursive scroll
#

we were given this problem for implicit differentiation and I'm having trouble in figuring out the equation I'm supposed to be using and in general just trying to illustrate the problem in my head

cursive scroll
#

the previous problems given to us already had an equation, but most of them were functions that can be graphed, this problem awfully seems like a one-dimensional equation though..? correct me if im wrong

#

I need some help in just illustrating the problem so I can understand it better

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main cargo
obtuse pebbleBOT
main cargo
#

idk how to work out P(AnB')

#

a and not B

#

on a venn diagram, how would that be shaded?

#

like that?

#

although

#

i dont think you can use a venn diagram for this

slim leaf
#

P(B') = 1 - 0.6 = 0.4

main cargo
#

how do i get anb' from there

#

i cant multiply by a

#

because its not indipendent

slim leaf
#

Yes

main cargo
#

i know this formula

#

i could use this

#

but then i need to know P(aUb')

#

i dont even know what aUb' means

#

a or not B?

slim leaf
#

Yeah

main cargo
#

how would that be on venn diagram?

#

at a guess?

#

or am i wrong

#

wait,

#

i think it might include the middle?

#

idk

slim leaf
#

Ah

#

I think you have to use P(A' | B) = 1 - P(A | B)

obtuse pebbleBOT
#

@main cargo Has your question been resolved?

twilit ivy
main cargo
twilit ivy
main cargo
#

the diagram is P(AnB')

twilit ivy
#

thats correct

main cargo
#

thanks

#

.close

obtuse pebbleBOT
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sonic cape
#

hi could anyone suggest a reason for why the solution applied e^x to determine whether the estimate is accurate or not

sonic cape
#

The solutions for part a and b are here if it helps

dull rune
#

its showing how useless the upperbound is

#

cause ln(e^4) = 4

obtuse pebbleBOT
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ember vigil
#

I’m confused with everything, can anyone help?

midnight topaz
ember vigil
#

Bruh im stupid as hell this is fine

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.close

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ashen sierra
obtuse pebbleBOT
ashen sierra
#

How do I make dy/dx the subject?

grizzled shore
#

you would first need an equal sign

tulip thicket
#

a bit of algebra I thinj

ashen sierra
grizzled shore
#

monkaw that's an equal sign?

ashen sierra
ashen sierra
brazen saddle
#

,rotate

warm shaleBOT
brazen saddle
#

Reckon this is the question

ashen sierra
#

yep same thing

grizzled shore
#

Does this look good

ashen sierra
#

thank you vm

grizzled shore
#

usually when things are complicated

#

substituting simple variables make it much easier on the eyes

ashen sierra
#

thank u, ill keep that in mind for future questions 🙂

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cinder quiver
obtuse pebbleBOT
cinder quiver
#

i dont get it :(

high lily
#

which part don't you get

cinder quiver
#

all of it

high lily
#

this question is all about basic definitions/types of triangles

#

do you know what a scalene triangle is?

cinder quiver
#

no

high lily
#

do you know anything about types of triangles listed?

cinder quiver
#

its our first classwork about it i didnt seem to pay a lot of attention lol

high lily
#

do you have notes?

#

or just google each name in that list

cinder quiver
#

i have some but not about that topic i think ima check tho

cinder quiver
#

yeah i still dont get it

#

is this part i did right?

#

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hexed agate
#

very goo question you got

timid silo
#

yo

obtuse pebbleBOT
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tulip thicket
#

(x+x^-1)^2

#

that would be x² + 2 + x-²

#

etc

#

factor the top side

#

yes

#

no

#
  • not -
#

now factor out the x'es

#

divide etc

#

factor the numerator into parts that can be divided by the denom

tulip thicket
#

numerator becomes (x+x^-1)² -3

#

,w factor x^2 + x^-2 -1

warm shaleBOT
obtuse pebbleBOT
#

@timid silo Has your question been resolved?

obtuse pebbleBOT
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@timid silo Has your question been resolved?

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ionic kite
obtuse pebbleBOT
ionic kite
#

So basically this was a meme but I felt like answering it anyway bc why not

#

This was my answer/response to the question

#

Is it correct?

kind hawk
#

well that depends on how you interpret the question. would it take more players less or more time to play the same thing (if we are already ignoring that it doesn't make sense)

ionic kite
#

It's a question from my exam board, the topic is direct and indirect proportion

#

But yh ur right overall we won't know

kind hawk
#

well it's a picture from a tweet. with the context that a teacher asked a bunch of these questions with the note that one of them makes no sense so their students wouldn't just blindly do some stuff without thinking

ionic kite
#

True Idk I just felt some urge to answer it 😭 😂

#

Anyway might as well close this

#

.close

obtuse pebbleBOT
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brave bramble
#

There is an answer, it's still 40 mins. It's not like more players make it faster

kind hawk
#

no the real answer is that there aren't enough people to play it 😛

brave bramble
#

For a question like this that actually makes sense:
"6 people can dig 4 holes in 2 hrs. How many holes can 10 people dig in 4 hours?"

kind hawk
#

(i don't know how many players that piece of music "needs")

brave bramble
#

Oh, yeah that makes sense too I accept it

ionic kite
#

Logically that makes sense

#

But maths wise no

#

U need to use a fOrMuLa to work it out

obtuse pebbleBOT
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lyric iron
#

Does anyone wanna try work through this with me? I'm lost.

obtuse pebbleBOT
#

@lyric iron Has your question been resolved?

drowsy girder
#

$$e^{\frac{-1}{x^2}}$$ as x approaches 0

warm shaleBOT
#

Pluton

lyric iron
#

but with the amount of difficulty everyone is experiencing, i think its deeper than that

#

IK the value of a is 0 since the function has to be continuous everywhere, and f(x) = a if x = 0

#

but i cant explain it using calculus

#

i am not smart enough

versed turret
#

For $f(x)$ to be continuous, $∀a ∈ D, f(a) = \lim_{x \to a} f(x)$. ($D$ is the domain.)

#

Continuity is a condition for differentiability, so we can see that $a = \lim_{x \to 0} f(x) = \lim_{x \to 0} e^{-1/x^2} = 0$

warm shaleBOT
#

castroploiin

#

castroploiin

obtuse pebbleBOT
#

@lyric iron Has your question been resolved?

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normal wind
obtuse pebbleBOT
normal wind
#

can someone please help me understand this
Is the error same as standard error ?
if so, ho is error = |x bar - u | / sigma / sqrt(n)
isn't should be only sigma / sqrt(n)

obtuse pebbleBOT
#

@normal wind Has your question been resolved?

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warm gust
#

Does my approach look correct? Just having trouble with my limits of integration.

obtuse pebbleBOT
#

@warm gust Has your question been resolved?

rigid pine
#

Then you'd have 0 <= r <= 1 and 0 <= theta <= 2pi.

warm gust
#

I am a bit lost as to what I am doing. I am trying to find the outward flux on the surface so I used the left side of the divergence theorem. I am just a little lost with how r is [0,1]

obtuse pebbleBOT
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warm gust
#

.reopen

obtuse pebbleBOT
#

rigid pine
#

0 <= r <= 1. For, you cannot have a negative radius.

warm gust
#

Oh i see what I did wrong

rigid pine
#

Nice. 🙂

warm gust
#

Wait why is there an r in your parameterization for X and y.

rigid pine
#

You're parameterising a surface.

#

You need to get the points within the intersection curve.

warm gust
#

I thought ellipse was X=acost Y=bsint

rigid pine
#

Yes. You are within this ellipse. The surface is the part on the plane z = 4 - y within the elipse.

warm gust
#

Oh wait am I just calculating the intersection?

#

Oh nvm graphed it in Georgebra I think I get it now

#

Thank you

#

.close

obtuse pebbleBOT
#
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cursive bridge
obtuse pebbleBOT
timid silo
#

your math question in a clear, concise manner.* ?

cursive bridge
#

alright give me a second so i can type it out.

#

or should I just take a closer picture for each problem?

timid silo
#

i can help with the first one now

cursive bridge
#

alright

#

?

hexed agate
#

Do you know equation of a straight line?

#

Lucid?

cursive bridge
hexed agate
#

y=mx+b

cursive bridge
#

oh yeah i know that

hexed agate
#

So what is b?

#

So you know what it represents? And also what is m?

cursive bridge
#

to be honest with you I don't remember what they specifically mean

hexed agate
#

No worries

cursive bridge
#

cause we went to a new unit but im doing corrections right now so its been since the beginning of the year since ive done it

hexed agate
#

m is the slope of the graph. Outside USA we call it the gradient of the graph

cursive bridge
#

alright let me take notes

hexed agate
#

Do you know how to find it?

cursive bridge
#

could you refresh me?

#

on how to

hexed agate
#

(y2 - y1)/(x2-x1)

cursive bridge
#

isnt that the one of the versions of the Pythagorean theorem?

hexed agate
#

Not really

cursive bridge
hexed agate
#

You are finding the slope which may also be referred as rise over run

cursive bridge
#

the first question is asking me to write an equation for the graph

hexed agate
#

Yes

#

Now let's do that

cursive bridge
#

alright

hexed agate
#

Which one is the x variable and which one is the variable y here?

#

Between c and t

cursive bridge
#

Umm how would I find that here

#

like whats in the middle?

hexed agate
#

Well, y is always the vertical line, the dependent variable

#

X is the horizontal line, the independent variable

cursive bridge
#

alright just marked those down as X and Y

hexed agate
#

We call them x and y axis

#

So c is the y axis and t is the x axis

#

Get it?

cursive bridge
#

yes

hexed agate
#

So your equation would look something like c=mt+b

#

But we are not done

#

We need to find m and b

cursive bridge
#

alright

hexed agate
#

One more thing do you know how to write a point on the graph?

cursive bridge
#

yes

#

write a dot where the specific coordinates are right?

hexed agate
#

Yes

cursive bridge
#

alright then i do

hexed agate
#

You right like (x, y)

#

Like (0, 0)

cursive bridge
#

yeah i know that

hexed agate
#

(500, 5000)

#

Good

#

Now to find the slope take any two points on the graph

#

Any two points you like

cursive bridge
#

500,1000

hexed agate
#

Write in brackets clearly

#

In the form of (x, y)

cursive bridge
#

ok

hexed agate
#

Like (0, 0) is a point

#

On your graph

cursive bridge
#

so dot (500,1000)?

hexed agate
#

Just to be clear the points where the line pass through

#

In (500,1000) the line doesn't pass through

#

(500, 5000) it does

#

Shall we pick that ?

cursive bridge
#

alright yeah

hexed agate
#

Ok so let (x1,y1) = (0,0) and (x2, y2) = (500,5000)

#

Now according to the slope formula I showed you prior

#

5000-0/500-0

#

Which is 10

#

So we got m = 10

#

Got it?

cursive bridge
#

im confused

cursive bridge
hexed agate
#

I used the formula (y2-y1)/(x2-x1), plugged in the valued and did math?

cursive bridge
#

no no no no i mean like what do you do with that

#

like do i plug it in something

#

or is it just there for when we do something else

hexed agate
#

So you understand how I got m = 10?

cursive bridge
#

no

hexed agate
#

5000-0 is 5000

#

Divide it by 500-0

#

Which is like 5000/500

#

Which is 10

cursive bridge
#

ooooohh ok I get it now

hexed agate
#

So we found m

#

Now b is the y intercept

#

Y intercept means what is y when x = 0

#

In this example it is very easy because when x=0 y is also =0

#

So b = 0

#

Get it?

cursive bridge
#

yes

hexed agate
#

So as we know c=mt+b

#

We plug what we found

#

c=10t+0

#

c=10t

#

That is the equation of the graph

cursive bridge
#

alright thanks

#

makes way more sense then it did earlier lmao

hexed agate
#

Sorry if I was annoying. I was trying to explain super slow so that you get it

cursive bridge
#

it wasn't annoying at all

timid silo
#

hi idk if i already wrote here but

#

where can i find someone who will help me in stereometry

cursive bridge
#

i can close this channel for you so you can use it

timid silo
#

what does it mean

#

im new here so

cursive bridge
#

or go to the category that says Math help available

#

and type what you need help with in the two channels that are available

timid silo
#

thank u

cursive bridge
#

np

obtuse pebbleBOT
#

@cursive bridge Has your question been resolved?

obtuse pebbleBOT
#
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lament frost
#

Hi, I need help with the following question: The expression x^3 + 7x^2 – 3x + 12 has a remainder of –9 when divided by x + k. Find the
possible value(s) of k.

grizzled shore
#

Do you know polynomial long division

fierce lagoon
#

This is certainly a moment

#

Let's see

#

$$\frac{x^3+7x^2-3x+12}{x+k}$$
$$\frac{x^3+kx^2}{x+k}+\frac{(7-k)x^2-3x+12}{x+k}$$
$$x^2 + \frac{(7-k)x^2-3x+12}{x+k}$$
$$x^2 + \frac{(7-k)x^2+(7-k)kx}{x+k} + \frac{(k-4)x+12}{x+k}$$
$$x^2 + (7-k)x + \frac{(k-4)x+12}{x+k}$$
$$x^2 + (7-k)x + \frac{(k-4)x + (k-4)k}{x+k} + \frac{(16-k)}{x+k}$$
$$x^2 + (7-k)x + (k-4) + \frac{16-k}{x+k}$$

I'm gonna edit this as I go; feel free to look at my work as I edit this

obtuse pebbleBOT
#

@lament frost Has your question been resolved?

warm shaleBOT
#

Umbraleviathan

fierce lagoon
#

I think you know what to do from there

#

Ping me if you have questions

obtuse pebbleBOT
#
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obtuse pebbleBOT
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red lark
obtuse pebbleBOT
red lark
#

how did we arrive at the third last step?

rancid dust
#

dont helpers

#

its not been 15 minutes yet

red lark
#

sorry

slate cosmos
#

Cross multiplied?

red lark
#

but like

#

where did the tan come from?

warm canopy
#

1/cotx = tanx

#

If I'm correct about where you're confused

red lark
#

are we cross multiplying it?

#

ahhh ye

warm canopy
red lark
#

ye

#

i get it now

#

thanks @warm canopy

#

.close

obtuse pebbleBOT
#
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tacit briar
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What's the expected value of the product of a six-sided die times an eight-sided die?

tacit briar
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i basically find the EV of the six sided die, and the EV of the eight sided die

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<@&286206848099549185>

tardy epoch
tacit briar
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would that be right?

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EV of six sided die is 21/6

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EV of eight sided die is 29/6

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(EV of six sided die)(EV of eight sided die) = 203/12

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@tardy epoch

obtuse pebbleBOT
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@tacit briar Has your question been resolved?

tacit briar
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<@&286206848099549185>

obtuse pebbleBOT
#

@tacit briar Has your question been resolved?

obtuse pebbleBOT
#
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odd frigate
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I’ve tried to solve this problem but I keep getting the incorrect answer what did I do wrong?

obtuse pebbleBOT
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@odd frigate Has your question been resolved?

odd frigate
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<@&286206848099549185>

lime cypress
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I would have done u-substitution

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Wait nvm

obtuse pebbleBOT
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@odd frigate Has your question been resolved?

obtuse pebbleBOT
#

@odd frigate Has your question been resolved?

past nexus
finite vector
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As per ur photo the answer's correct

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But u haven't highlighted the same in the options

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Probably missed a - sign

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From ur last step

brazen saddle
obtuse pebbleBOT
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@odd frigate Has your question been resolved?

obtuse pebbleBOT
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obtuse pebbleBOT
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timid silo
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$2x + \frac{2}{x} = 3,$ find $x^3 + \frac{1}{x^3} + 3$

warm shaleBOT
timid silo
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so first I turned it into a quadratic

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$2x^2 -3x + 2 = 0$

warm shaleBOT
timid silo
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but when I tried to solve it using the formula the determinant becomes negative

devout solar
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so we are supposed to find what x³+1/x³+3 is?

timid silo
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I'm wondering if I should solve it the obvious way (find x then substitute it for x^3) or if there's another easier way to do it

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does x have to be real?

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oh

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I'm dumb

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there's an easier way

devout solar
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I know

timid silo
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substitute x^3 = t

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wait no

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nvm

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ok

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I thought about functions

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the left expression can be written as x + 1/x = 3/2

timid silo
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which is very similiar to the right one

timid silo
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find the value of x+1/x

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so I thought maybe some sneaky sub or something

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then find of x^2+1/x^2

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multply them

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and form an equation

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u will observe a pattern

fierce lagoon
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Bruh this is easy

compact shadow
warm shaleBOT
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Cogwheels of the mind

fierce lagoon
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Ihold on hold on

compact shadow
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And you know that x+1/x=3/2

timid silo
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where did you pull out this identity from wth?

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$x^2 + \frac{1}{x^2} = \frac{1}{4}?$

warm shaleBOT
fierce lagoon
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Divide the left side by 2, you get

$$x+ \frac{1}{x} = 1.5$$

The right side is

$$x^2\left(x+ \frac{1}{x}\right)+ 3$$

$$1.5x^2 + 3$$

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Wouldn't this be easier

compact shadow
fierce lagoon
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Oh wait

timid silo
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you can't factor out that x^2 like that tho

fierce lagoon
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Im actually

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Im atcuslly@mentally stupid

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I did not just say that x^2(1/x) = (1/x^3)

timid silo
fierce lagoon
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You be quiet lmao

timid silo
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ahh I got so close

compact shadow
timid silo
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$x^3 + \frac{1}{x^3} + 3 = \frac{15}{8}$

warm shaleBOT
timid silo
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the thing is

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15/8 is not one of the options

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but 15/4 is

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it's probably a silly mistake I'll check

compact shadow
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I got 15/8

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And didn’t solve for x

timid silo
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,w 1/4*3/2-3/2+3

timid silo
compact shadow
timid silo
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i get 21/4 lol

nocturne minnow
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I got pi/e

timid silo
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actually no I'm dumb

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nvm

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ok now I got 35/8

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I just cubed ( x + 1/x)

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to get x^3 + 3 x + 3 1/x + 1/x^3

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and then simplified that to

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I did it like

$x^2+\frac{1}{x^2}=\frac{1}{4}$

$(x+\frac{1}{x})(x^2+\frac{1}{x^2})=\frac{3}{8}$

$\implies x^3+\frac{1}{x^3}+x+\frac{1}{x}=\frac{3}{8}$

$\implies x^3+\frac{1}{x^3}=\frac{3}{8}-\frac{3}{2}$

$\implies x^3+\frac{1}{x^3}+3=\frac{15}{8}$

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(x^3 + 1/x^3) + 3 * (x + 1/x) = 27 / 8

compact shadow
timid silo
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plugged in x + 1/x = 3/2

timid silo
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I have

compact shadow
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Thanks

timid silo
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and then from there got x^3 + 1/x^3

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where did I go wrong to get this answer tho?

warm shaleBOT
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a^3+b^3=c^3 has a whole no sol.

timid silo
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is to cube it

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like u did

timid silo
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ok now I get 3 as an answer after finding a mistake

timid silo
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@compact shadow doesn't the formula u used also comes from adding and subtracting the thing left outside the cube and factoring one part right?

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I really just did

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8/2 = 3

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I need profesional help

timid silo
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take some rest

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highly reccomended

timid silo
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so are we all coming to an agreement that the answer in my book is wrong lol

timid silo
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oh crap

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literally all of us

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I didn't notice

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came with the same thing

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there is an option for none of these

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lmao

timid silo
timid silo
# timid silo

I think cubing it is kinda tedious I always avoid cubing

timid silo
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yeah but in this case

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it sorts out nicely

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I think Cogs method

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is most suitable

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if it works it works

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still tedious because you have to go through the whole identity again

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anyways

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thank you all

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.close

obtuse pebbleBOT
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charred remnant
obtuse pebbleBOT
#
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timid silo
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ok i have question

obtuse pebbleBOT
timid silo
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W = 2/s squared + m

i’m having trouble making m the subject

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the squared s is putting me off

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ignored 💀

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dumbass💀

warm canopy
timid silo
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trolling trolling

warm canopy
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?

high lily
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$W= \frac{2}{s^2} + m$?

nocturne minnow
warm shaleBOT
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ℝamonov

nocturne minnow
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Or I think ramonov can maybe close it too

warm canopy
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Aight

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.close

obtuse pebbleBOT
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warm canopy
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Wow help 9 was a mad read

nocturne minnow
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And I literally linked the help channel 3 times

obtuse pebbleBOT
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paper coyote
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If we assume there is a pdf such that
f(x) = a.g(x) + b.h(x)

where g(x) and h(x) happen to be exponential distributions with rate L1 and L2, and a and b are constants set such that the integral from 0 to infinity of f(x) = 1.

I asked a question about the expectation a couple of days ago, and was told to consider the unconscious statisician and linearity of integration.

I did this, and I'm happy that by E[kx] = kE[x] and E[x] = 1/lambda for exponential distr, I can say that in this particular case:
E[x] = a.1/L1 + b.1/L2.

I also did this by integrating from 0 to inifinity of x.f(x) in Wolfram Alpha and I get the same number, so I'm pretty confident that's right.

Now for a bit of an inductive leap. Seeing as Var(x) is defined in terms of E[X] (or E[X^2]) I thought I could use the same principle for the variance. Knowing that Var(x) = 1/Lambda^2 for the exponential distribution, and that Var(kx) = k^2.Var(x), I tried
Var(x) = a^2 . 1/L1^2 + b^2 . 1/L2^2

This gets me 1/2 of what I calculate by just generating lots of samples and working it numerically. So, should there be a 2x somewhere, and if so, why? Should I consider somehow the Covariance even though there's only one 'x' ?

paper coyote
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That's perhaps unclear, I'll try to reformat in latex

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$Var(x) = a^{2} \cdot \frac{1}{\lambda_1^{2}} + b^{2} \cdot \frac{1}{\lambda_2^{2}} $

obtuse pebbleBOT
#

@paper coyote Has your question been resolved?

obtuse pebbleBOT
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radiant juniper
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2 +2

obtuse pebbleBOT
dawn meteor
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👀

radiant juniper
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mhm

dawn meteor
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what base

radiant juniper
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wdym'

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.close

obtuse pebbleBOT
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obtuse pebbleBOT
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viral orchid
obtuse pebbleBOT
hexed agate
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yes simpify

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what have you tried?

viral orchid
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im blank

hexed agate
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you add two fractions

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how do you add two fractions?

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like 5/7 +9/8?

viral orchid
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yes

warm canopy
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how

obtuse pebbleBOT
#

@viral orchid Has your question been resolved?

#
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languid valley
#

Integral arctan (8x-4) dx = x * arctan (8x-4) - 1/2 (8x-4) * ln (x²+(8x-4)²) is this correct?

kind hawk
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check with wolfram alpha

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you forgot the constant of integration

languid valley
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Oh yeah

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but idk Wolfram isnt really helping me

kind hawk
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,w integrate arctan(8x-4)

warm shaleBOT
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Failed to get a response from Wolfram Alpha.
If the problem persists, please contact support.

lean sigil
languid valley
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uh

kind hawk
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difference of that and your answer is not a constant

languid valley
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no I think there is a difference

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I totally forgot we got send an answers paper anyway but I'm still confused

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the answer is 1/8 (8x - 4)*arctan(8x-4)-1/16 ln((8x-4)²+1)+c

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Im just confused where the 1/8 comes from

kind hawk
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inner derivative probably

languid valley
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wdym exactly

kind hawk
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well somewhere in that whole mess when differentiating we will get the inner derivative of 8x-4

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to compensate for that we need a factor of 1/8

languid valley
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hm well the easiest way to solve it is with a book anyway

kind hawk
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or from the other direction when you do the u-sub u=8x-4 you also get 1/8

languid valley
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I'm not studying mathematics I'm an engineering student so we're more than fine to use books if we can find the integrations in there

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but this should be it right?

kind hawk
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if it says it somewhere in a book, probably

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I'm notgonna check it

languid valley
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but thats still missing the 1/8

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or even how you get to the term ((8x-4)²+1)

kind hawk
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you use a u-sub u=8x-4 to get integral of 1/8 arctan(u) du

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then you apply that formula with x=u and a=1

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and then you sub in u=8x-4 again

languid valley
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oh ok finally

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now it makes sense

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I had an issue with another one however

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Integral (tan^3 x)/(1-sin² x) dx

obtuse pebbleBOT
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@languid valley Has your question been resolved?

kind hawk
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dunno. write 1-sin^2=cos^2. then maybe you have some integral of the form sin^n/cos^m in your book?

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or u=tan(x) ?

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yeah probably u=tan(x)

languid valley
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Yea well it goes correctly into 1/4tan^4x+c

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I just

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cos isnt a derivative of tan

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he does say it has something to do with addition theorems

kind hawk
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well what is the derivative of tan(x)

languid valley
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wasnt it something weird