#help-42
1 messages · Page 69 of 1
what about the d
trig sub
the problem is you'll get u^2 /d^2
v-sub lol
just make another substitution
yes
yeah but the d^2 is a problem
leave it be
if there is no information for d just leave it be, its just some constant
some shaky hands ....
$\frac1{d^2}\int\frac{\dd u}{\frac{u^2}{d^2}+1}$
is this what you meant
pay attention to the d, the upright d is different from normal d
no
$\frac{1}{d^2} \int \frac{du}{\left(\frac{u^2}{d^2} + 1\right)}$
RulzerFly
i meant this
∮μ²ƞdS
why there's no other way
∮μ²ƞdS
what about the d^2
it's not arctan(u)
d is just a constant
treat it like so
whats the formula for trig sub that you learned?
what's that you mean variable changing ?
yes
RulzerFly
RulzerFly
you mean the one with the tan
$\frac{d}{du} \arctan(u) = \frac{1}{1 + \tan^2(\arctan(u))}
$
$\frac{d}{du} \arctan(u) = \frac{1}{1 + \tan^2(\arctan(u))}$
RulzerFly
okay
$\int\frac{\dd x}{(x^2+a^2)^n} \to x=a\tan u$
∮μ²ƞdS
use this
a arctan u no ?
no
so du = 1/d dx
What the f i mixed everything together.....
$it's \frac{1}{d} \arctan\left(\frac{x + \frac{b}{2}}{d}\right) $
$\frac{1}{d} \arctan\left(\frac{x + \frac{b}{2}}{d}\right) $
$\frac{1}{d} \arctan\left(\frac{x + \frac{b}{2}}{d}\right)$
RulzerFly
i should be this no ?
finally ....
thanks for help (i know that i've given you headaches 💀 )
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Hi, i am a bit confused about the process on the right side- i understand why you want to multiply magnitude by sin and cos because the hypotenuse on the bottom will cancel out and you will simply have the x and y components, but how does this work for the 300N vector (the work done on the right) because there isnt really a triangle made here (and i know you could just look at and know its -300,0 but i kinda wanna understand how it works)
Better to think in terms of the angle, like the angle of F1 is 60 and the angle of F2 is 180, but if you think of it as a triangle it's effectively a triangle where the 'height'/'opposite' is 0 so the 'hypotenuse' and 'adjacent' merge into a single line
Like imagine what happens to the sides of this triangle as theta gets smaller and tends to 0
In the context of that diagram in your picture, their angle is measured from the +ve x, so is just 180-theta where theta is the angle in the triangle I drew
So as theta becomes 0, the angle in your diagram is 180-0 so just 180
Hence you arrive at the derivation of F2
Np!
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<@&286206848099549185>
do you know what a circle is
what about the center of a circle
the radius?
no, the center
@crystal axle ^^
the point in the center of the circle
can you just tell me step by step of what to do
the red thing on the left is 2.5 ft
what's that red thing called looking at the second picture
radius?
so 5?
yes
2 x 2.5?
yes
.
yes
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diameter is already shown in diagram (1/4 or 0.25 yd)
radius is half of diameter = 1/4 * 1/2 = 1/8 yd
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145
,rotate
Where do I begin?
Yes
Ok so find a maximum for A = xf(x)
you want a maximum for the Area, so yes
svc
you can factorize e^(-x^2)
e^a is never 0 so you can already get rid of that term
(1-2x^2)(e^-x^2)
And only 1 of those could be 0
ab = 0 is the same as a = 0 or b = 0
set both equal to 0 maybe to avoid skiping step
(for example (x-3)(x-2)=0 is the same as x=3 or x=2)
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Ask a question
this is Arithmetic Progression
no wait
I read it as A_1 mb
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Hello
3rd root. ³√
Why not use this equation?
Like, the third root of 8 is 2.
So we can't use that equation for even roots?
That equation is being used
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I want to make a graph
where basically the mens 100meter world records
at on the y axis
and the date they were made on is on the x axis
but the thing i wanna do is
I have a theoretical limit of 8.97
so I want an asymptote
at 8.97
and I want the equation so that I can like predict future world records and when the theoretical limit will be reached
hmm it will be hard to fit something “useful” here
wdum
before anything i would want to see what the points look like, with race time plotted against date
this is what it looks like for swimming
I want something similar for running, but an asymptote
yea i get what you’re asking for
what platform should i use
i dunno, desmos or something if you just wanna see it, but eventually you’re probably going to need to put the data into some coding language with curve fitting support
is it doable on geogebra
or maybe wolframalpha will do it but you might want more customization than it offers
for seeing the points sure
does geogebra have the ability to create the function
hmm, is it not possible
is what not possible?
doing the plotting
and the software automatically just giving me a best fit line equation
well no software would use the plot, it would use the numerical datapoints
you need to be able to specify the conditions you want on the curve though
hmm
like as an example you might ask it to find the “best” fit among curves of the form y = ae^(-bx) + 8.97
so a and b are something the software would compute
or you can ask it for some other type of curve with an asymptote, not necessarily an exponential function like that
oh
got it
makes sense
thats yeah
ok
makes sense
you can also try just plotting the points in desmos and playing around with a and b until you find ones that look ok if you want a lower effort “solution” lol
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find all the value for a and b so that u v w are linearly independent.
I tried using ERO but still can't get the value for a and b respectively
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@marsh blade Has your question been resolved?
Opposite over hypotenuse is the sine
we took sin theta= y/15 since sin theta = opposite side / hypotenuse
Also if your wondering why we only took sin theta it is because we need to compare the theta with something that is variable in the problem. Since the height is varying we took sin theta so that theta can be compared to the rate of change of the height.
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Im getting 54 for 5d is it correct?
<@&286206848099549185>
So there are 3 numbers at start to make it greater than40000
So 3 at start
Then 4 num left
Hmm
Out of which 3 can make it even
What does that mean
@rich ore Has your question been resolved?
<@&286206848099549185>
@rich ore Has your question been resolved?
I would suggest considering three cases
i) Those who start with a 4
ii) Those who start with a 5
iii) Those who start with a 6
And then you can add up the amount of solutions for each of the particular cases
Wont that be lengthy making each permutation individually might even miss some
No, it will be in fact easier
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Guys, does anyone know how to find the volume of solid of revolution bounded by two functions, if one of the functions is negative on some interval and positive on the other?
To be more concrete, here's the problem I was trying to solve:
But I'm worried this solution may over or under count the actual volume
Maybe computing it as
$$
\pi \int_a^b \left| f^2(x)-g^2(x) \right| , dx
$$
will fix the issue?
Sweet Tea 🧋
so if that part of the shape isnt contributing any volume (basically it would be going over part of the volume traced out by the upper part of the function) then you can just ignore it altogether
Hmmm. I think I can see that (at least if we were given only the parabola without the line), but I'm not sure if that works when we have 2 functions as well
if you wanted to be technically correct you can show that | lower function | <= | upper function | on the given interval
calculate the shape as usual, but subtract the redundant volume
Yeah, yeah. I get the idea. But again, I'm not sure abt this: #help-42 message
which redundant volume and how as usual? 
so you can just consider the volume traced by this region and set your bounds accordingly or do what fungus suggested and subtract the redundant volume, i guess whichever you think would be easier to set up the integral
if you revolve the graph around the x-axis, you can see that there is a portion that is revolved twice
thats the redundant volume
calculate that too
for this ^ way (as in picture) you can do the intgral of line - parabola from first interseciton to x = 0 then just integral of the line function between 0 and the 2nd x intercept, then integral of line - parabola on the right
like these 3 regions will have different setups
Oh, I see! Thanks! 
So this is usually done just by eyeballing it?
Like, no 'universal' formula? 
I think
$$
\int_a^b \left|f(x)-g(x)\right| , dx
$$
for computing the area bounded by f and g on [a, b] will always work, for example
Sweet Tea 🧋
I mean, the regions that we'll split our function into
well that still applies on the interval [left intersection of the functions, 0] and [2nd zero of the parabola, 2nd intersection of the functions] and on the one in the middle its just area under a single graph which you know the formula is just a basic integral, but yeah you just to consider what is bounding the region i guess that's all
you can also do what fung suggested, both setups are pretty easy to work with i would say
wait, how do you mean that still applies?
those are two different things 
In the screenshot we are asked to find the volume of the solid of revolution
While the formula int_a^b |f(x)-g(x)| dif x gives the area (notice the absence of pi and f^2 and g^2)
I'm referencing this formula I've just sent
erm yeah sorry not area, use the volume equations
like pi (upper function^2 - lower function^2) dx isn't it?
lemme ask a separate (but still related) question then\
Why doesn't the formula
$$
\pi \int_a^b \left|f(x)^2- g(x)^2\right| , dx
$$
work in this case?
Sweet Tea 🧋
well that piece under the x axis like you say will be counted twice
since it traces out the same volume as its reflection above the x axis
which is already included
so what fung suggested is to just do the integral anyway, not caring about it being counted twice
hm, interesting. Bc I saw that on wiki and it didn't make any assumptions regarding whether f,g are positive or not
gotcha. I like yours method more tho 
can you show me where you are reading that on wiki
one moment
and then you would find the volume the rotation of this region creates and subtract it from the total
https://en.wikipedia.org/wiki/Solid_of_revolution
(It's described for revolution around y-axis, but I guess it also works when we revolve around x-axis)
In geometry, a solid of revolution is a solid figure obtained by rotating a plane figure around some straight line (the axis of revolution), which may not intersect the generatrix (except at its boundary). The surface created by this revolution and which bounds the solid is the surface of revolution.
Assuming that the curve does not cross the ax...
this is the problem
actually thats maybe about something else
Also, do you know of a few (like one or two) exercises for this idea (when a function crossess the axis), preferably with answers
Just want to make sure I got it 100%
ok that quote was a bit about something else, but yeah this discussion is when the generating curve is not crossing the axis
the generatrix i guess is the curve used to generate the volume so like your function basically, in your case one of these generating curves is in fact crossing the axis of rotation
so you can see why that generates issues :d
i dunno, are you learning from a book? otherwise maybe you can google stuff, i dont really have any examples at ahnd myself
@proud egret you could have something like this where if you are rotating these regions over the x axis and considering volume, well you wouldn't have any issues because neither of the regions has a reflection over the x axis so they would both just be contributing their volume as normal, what you have to consider is just if the area you are rotating has a corresponding area reflected over the axis of rotation, thats what you need to consider
<@&268886789983436800>
@proud egret Has your question been resolved?
I'm not closing yet because I'm still working on an example I just came up with to test my understanding
I hope to continue the discussion from here in case I have any difficulties 
@proud egret Has your question been resolved?
Ok, so, here's an example:
I'm trying to properly find the V(sol. of rev. of the green shape when rotated around x-axis)
The functions are given by f(x) = x/2 - 5 and g(x) = -1/10•(x-10)^2 + 5
I'm a bit confused how to approach it.
Do I like draw y=|f(x)| and y=|g(x)| first and try to eyeball it from there?
the thing I'm a bit confused it that it isn't always that easy to determine what function will have «greater magnitude»
In this example, we'll have
$$
|f(x)|\ge |g(x)|, \quad \forall x \in [0, 5]
$$
but then it changes:
$$
|f(x)|\le |g(x)|, \quad \forall x \in [5, 15]
$$
Sweet Tea 🧋
I've drawn the abs values of the functions (red is $|g(x)|$ and blue is $|f(x)|$) \
And it doesn't look that easy to actually find out when we just have to do $\pi \int_a^b h^2$ and when $\pi \int_a^b h^2 - u^2$ (where u is just a function, I've ran out of letters xDD)
Sweet Tea 🧋
<@&286206848099549185> ||just in case you only get a notification only when a new help channel is opened||
What do u need help with
Calculating the volume of the solid formed by the shape shaded in green, when revoled around x-axis
In particular, I'm a bit confused how to apply the disk method
$$
V=\pi \int_a^b f^2-g^2
$$
when either the functions cross the x-axis or when it isn't true that one of them is always (on the interval $[a, b]$) greater than the other
Sweet Tea 🧋
@proud egret Has your question been resolved?
@proud egret hm for this one seems like it'd be easiest to just like find the volume overall including the overlapping part and then subtract what is counted twice, i think the picture you drew earlier is helpful
like subtract this part here that is the volume generated by these two regions, the red is a bit easier since its a triangular region that will generate a right circular cone which you dont even have to integrate, you can use the volume formula for a cone, then you can find the volume generated by that blue region using the quadratic
ping me if you're back / still need help later
Oh, thank you for the reply!
Honestly, I don't have intuition of what you are trying to communicate to me 
its just same idea as previous problem we discussed, thats the part of the region being rotated that has a reflection on the other side of the x axis so both parts arent necessary to create the whole volume
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Anyone able to help with beginner scripting in python? Or know a place to get help?
It’s not a question it’s wanting me to write code and idk where to start or what to do. I’ll send pics
I can suggest freecodecamp.org ............... it's free
I’ll check that out!
It’s for a college course that’s kicking my ass lol
I’m a geology major, I get why they’re having me learn it but I’m drowning out here
FR
GEOLOGY !!!, I'm CS student and yet this rubbish is swallowing me
you've got it hard bro
F
It’s not even that I don’t think it’s interesting, I just have a small lizard brain that doesn’t understand math lmao
Drowning together 
that's fine, even though i study cs, 90% of my study is math and electronics, and 10% left is filled with a bit of useless pascal programs
anyways close the channel or the mods gonna get mad 
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can anyone prove that sinx + cosx*√3 = 0
,w graph sin(x)+cos(x)*sqrt(3)
,w graph 0
Do you need to prove this or find x where this eq holds true
Cause I don't think this equation can be proven for all x
find x where the equation is true
I'm actually kind of stuck in the middle of a math and I know the answer to this should be zero?
Can I see your work?
yea hold up
This is the math actually which should be equal to -3/4*sin3x
I've already got the answer but there's this part left so i thought it should be equal to zero
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I'm asked to show condition work/state conditions met or not met etc.
bit confused, I know that the conditons are
f(a) exists
limf(x) exists
f(a)=limf(x)
how do I find the value at which it is continution/not continuous
for a it is quite obvious being 3
but how would I prove the 2nd condition
f(3) DNE fine
wait lmme try smth
.close
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When our bottom is equal to zero, the function is not continuous or discontinuous
It becomes a vertical asymptote
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@full mirage Has your question been resolved?
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I'm noticing the transition points -2 and 0
so what I tried was
$2=\lim_{x\rightarrow -2}(ax^2+b)$
Remlis
Yep
$2=4a+b$
Remlis
And we also need b=6
Yes
Basically we want all the boundary connections to be smooth
Thats the goal of these types of problems
And then we solve for a
Remlis
$-4=4a$
Remlis
$a=-1$
Remlis
Yes
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@vivid surge
They closed that channel
oh
yeah it is
The formal is 0, 1
it's wrong ;-;
I solved like one hour ago 😢
this is correct
Thanks
i think the answers given might be a typo
Yeah maybe thank you 😊

!done
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copy paste it
.close
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how do i do a
if f'(x) is in the positive area what does that tell us
ohh that its increasing?
yep
what about b?
is it concave down because as x --> infinity the values reach 0?
it is concave down
but why
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no
Npnp
.close
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I don't understand how they got the domain and range of the bottom one
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how did he go from first step to 2nd
like ik how he removed the 2 down there by taking out 1/2
but how did he move the e^x up and made these stuff
if you are studying integration then you just know it
basic rules of exponents?
- when a constant is a coefficient of all the variables you can factor it
- dividing 1/e^x is same as multiplying the reciprocal
$\int \frac {e^{1.5x + 3.5} + e^{2x}}{\frac {2}{e^x}} \text { d}x= $0.5\int e^x \cdot (e^{1.5x + 3.5} + e^{2x}) \text { d}x$
$\int_{ }^{ }\frac{\sqrt{e^{3x+7}}+\left(e^{x}\right)^{2}}{\frac{2}{e^{x}}}dx=0.5\int_{ }^{ }e^{x}\left(e^{1.5x+3.5}+e^{2x}\right)$
ren
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Hello
My answer is SDZBGDQ
And there is no such option
From the first example of student
I thought it just changed the letter and put the letter preceeding it
S is replaced by R because it is before it and T by S and so on
And hence C should have been replaced by B

observe that the 4th letter changes successively
this question is...
oh shit you're right
I only went for 3 letters and stopped
Thank you
then the fourth answer is correct
Thank you
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What should I do after this
Stuck with it from yesterday
I've got 4 equations but it turns out to be a loop
Question? 🙂
Ohhh
why does noone read what i say
Did you write anything above?
I've read
About?
what are you saying I don't get anything
The meaning of this
Oh, my bad
And he suggested us to read adventitious triangle
but that problem and this problem is a bit different
and I'm stuck in the midway
@shy light Has your question been resolved?
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Why they did (A-7I) and not
$\frac{Ax}{7}$
Eigenvalues
i haven't done eigenvalues but what use is this? Lol
to show that there's nontrivial solutions, you have to show that Ax = 0 for nontrivial x's
so $Ax = \lambda x \rightarrow (A - \lambda \mbb{I}) x = 0$
nyxie9151
this "form" does exactly that
you show that there's a nontrivial x that solves (A - lambda* I)x = 0
which is equivalent to showing that the determinant (A - lambda*I) = 0 or the columns/rows are linearly dependent
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wth
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could anyone explain this terrible markscheme to me please 😭
@midnight thistle Has your question been resolved?
if they intersect at a point, then y of the line equals y of the curve
y = k - x = 6 - (x-3)^2
after some simplification and rearranging u will get a quadratic equation that must have two roots
cuz he says that it intersect at two different points
the roots of the quadratic I get don't give me the answer though
show me
also the roots will have the variable k in it
thats why he make sure that
b^2 - 4ac > 0
i rearranged k-x = 6 - (x-3)^2
to k-x = x^2 -6x - 3
to
0 = x^2 - 5x - 3 - k
there is a negative sign in front of the ()
6 -( x^2 - 6x +9)
oh i see so it should be -x^2 - 6x - 9
+6x *
i see so then that simplifies to x^2 -7x + (3+k) but then how do i find the roots of this
in order to have two roots, the value of b^2 - 4ac should be greater then zero
i see so now i have worked out the first value of k for 37/4 but how do i work out the lower bound
thats what im trying to figure 😂
one way is to say k = x + y
= 3 + 2sin(t) + 4 + 2cos(2t)
thats quite hard to solve lol
calculus is one way if u know it
i do understand calculus to a degree
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isnt L1 = 2???
what?
and arent Lucas numbers defined by Ln + Ln+1 = Ln+2
L1's value is defined as part of the equation
the 0th lucas number is 2
i think the indexing starts from 1
but okay lets just assume it starts from 0
in the question youve given, yes, which is why we have L_1 = 1
The Lucas sequence is an integer sequence named after the mathematician François Édouard Anatole Lucas (1842–1891), who studied both that sequence and the closely related Fibonacci sequence. Individual numbers in the Lucas sequence are known as Lucas numbers. Lucas numbers and Fibonacci numbers form complementary instances of Lucas sequences.
T...
on wikipedia we see n = 0 is defined as 2
why are the fibbonacci numbers in the DEFINITION of lucas numbers
i agree tho this is the standard definition
but since theyre equivalent, they chose to state the fibonacci version as "the definition"
yea okay so i jsut want to prove both direction right?
theyre only asking you to prove one direction
i think the proof will probably give u both directions for free
since ur showing that the two sequences coincide after all
yea eya
okey
let me try for some time
i just wanted to clear this doubt
yea sure
okay L3 = F4 + F2 = 3 + 1 = 4 is just false
OK
that is if L1 = 2
nah
the book is a bit badly written i guess
no problem
got it
kay thanks @inland vortex
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Can anyone help with this question?
compare the real and imaginary parts of the LHS and the RHS
z^3/4 = i
z^3 = i^4 = 1
take the cube root. you will get 3 solutions
some of them are extraneous
you will have to plug them back in
THis is the similar example we had in class but with a real number
I think I have to do a similar process to this
but how would I know the argument
you have 1 = r^(3/4) sin(3/4 theta)
you know r = 1, so this means sin(3/4 theta) = 1
you can solve that last equation in the usual way
How do we know r gives 1
I think I am missing something
look here
the magnitude of the LHS is 1, so the magnitude of the RHS is 1
thus r^(3/4) is 1
so r is 1
Ohh okie. How would i find the argument though to solve?
sin(3/4 theta) = 1
so 3/4 theta = pi/2 + 2pi n
where n can be any integer
now solve for the values of theta in say [0,2pi) that satisfy this
Where does this come from'? I know r is 1 but why does this make sin(3/4 theta) = 1
1
but wouldn't that mean 1(sin(3/4theta)
How do you arrive that 3/4 theta is pi/2 + 2pi n ?
Hmm I don't see how I thought that 1 was just for the imaginary part
I think I am forgetting some rule or something
can you clarify?
are you ok with the equation 1 = sin(3/4 theta) or are you confused about where it came from?
Yeah I am confused about where it came from
Like why multiplying the imaginary part by the angle gives 1
suppose i have an equation of the form:
a + bi = c + di
where a,b,c,d are all real
that mean:
a = c
and
b = d
now apply that to this equation
the left hand side can be written as 0 + 1i
and the right hand side can be written as $$r^{3/4}\cos(3\theta/4) + i r^{3/4}\sin(3\theta/4)$$
Bungo
so:
a = 0, b = 1
c = r^(3/4)cos(3 theta/4)
d = r^(3/4)sin(3 theta/4)
b = d gives you...
1
ohh that makes so much more sense now!!
Thank you : )
Does that mean I can just write the equation as r^3/4cos(3/4 theta) + 1
@pallid halo
if you want to use the cosine term, that's the real part of the RHS
so you'd want to equate that with the real part of the LHS
i.e.
you would be doing
a = c
in this case
a = 0, and c = r^(3/4)cos(3 theta/4)
so your equation would be
0 = r^(3/4)cos(3 theta/4)
which will give you the same solutions
When my prof did this example (a) she didn't get rid of the sin
@pallid halo
Is there any way I can do that for this question as well?
she did get rid of it
that's what is happening when going from the top equation here to the two bottom equations:
she wants r^15 = 2
and cos(15 theta) = -1
cosine is negative at pi
plus any multiple of 2pi
in other words, cosine is multiple when the angle is pi + 2pi n for any integer n
which you can rewrite as pi(2n+1)
okay so for this question how would I figure that piece out ? @pallid halo
like with 3/4 theta
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Need help on probability and statistics. Distribution of sample mean
which question
all of them
a should be obvious, the question tells you the parameters explicitly
yeah just realized it...
overthinked it
b should also be clear, you just need to take into account that your sample size is 14
so find the answer for b, it would be finding the standard deviation x bar?
I'm thinking to hard on this...
You have to find the mean and std dev yes
yeah so far
X = 64, STD = 20, N = 14
X x-bar = 64, STD X-bar= 5.34
I don't like X=64
isn't the 64 million the mean?
ah ok
Anyway, carry on
so overall I got STD and N correct but not X
64 looks fine to me
64 million as the mean, STD 20 million, N as the random sample is 14
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when i find the oblique asymptote, for example for the equation
$\frac{3x^2-2x-17}{x-3}$
i'd get $3x+7$
if a question asked "determine whether the curve approaches the OA from above or below"
with limit notation, how would I show the sides the equation approached the OA from
$\lim_{x->\infty}f(x) = (3x+7)^+$
would that be valid?
notnick
Now I don’t think so
At least I’ve never seen that notation or heard of that defined
What you can do is show that the equation can be written as 3x+7 + (something over x-3)
Maybe 4/(x-3)? Not sure
But anyway that goes to 0 when x is big
But this shows that the equation is always a bit above the asymptote
@trim ermine Has your question been resolved?
no not really, when you evaluate it goes to like 30000007
but yeah im not sure either
my teacher is a bit strange
as well as this textbook
like i could easily write "f(x) approaches the OA from above as x -> infty"
but that is a bit long
No I mean
The extra factor goes to 0
Dawg 😭
the OA is 3x+7
um 😭
$\frac{3x^2-2x-17}{x-3} = \frac{3x^2-2x-21}{x-3} + \frac{4}{x-3} = 3x+7 + \frac{4}{x-3}$
coak
Well you just have to ask yourself if 4/(x-3) is positive or negative for big x
Obviously it’s positive
So as x goes to infinity, the function will be just barely greater than 3x+7
But in the limit the difference is negligible and it goes to 0
Make sense?
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Why is this false? I can't find anything wrong with it except for the right integral missing a dx
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How do i do ths?
mb
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Well if 14y = 13k then surely y is a multiple of 13
gcd(13,14) = 1
in fact:
gcd(n, n+1) = 1
always!
25 - x is an integer
let that integer = k
14y = 13k
then divide both sides by 13
14y/13 = k
the right side is an integer because k is an integer
so the left side must also be an integer
then invoke euclid's lemma
13 is a prime, and if 13 | 14y, then either 13 | 14 or 13 | y
13 does not divide 14 because of what i said above about n being coprime to n+1
so 13 must divide y
25 - x is an integer
if a prime p divides the product ab, then p divides a or p divides b
here's an example:
3 divides 12 * 2, so either 3 divides 12 or 3 divides 2
is that not given?
So a natural number
If it’s true for integers then its then it’s true for counting numbers because counting numbers are a subset of integers
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why does lhopital only apply to indeterminate cases
if the limit is determinate, then you have your solution
.. to prolly simply put it, its because its not needed. its better to just direct substitution at that point
But why can it not be used
What makes it not work
Because it doesn’t work for determinant form
It’s not a matter of easier or harder
If you're interested in understanding why L'H doesn't work on conventional limits, start by understanding why L'H works for indeterminate ones, from a physical perspective
And why is that
Well if you don't know how the limits of a function's derivatives relate in a compartive (inf/inf or 0/0) case, its tough to figure out why it (might) fail when the limit is determinate.
What happens when you apply l'h to a limit that has already been solved by it? You get the wrong answer
Okay, but why
if I were to lhopital lim x->2 (2x+4)/x I would not get an undefined answer, I would get the wrong answer
What is so special about f(x) and g(x) being 0 that makes it work
If you decompose a regular l'h limit into its two consitituent functions, the visual intuition of l'h is that even though both f(x) values are zero, they have different rates of change. Since you have no initial "displacement", these rates of change dictate the nature of these two functions (or their ratio) in the neighbourhood of x=a
To illustrate:
Now, what if f(x) and g(x) don't match?
How does this show lhopital
I get the f(x) and g(x) being seperate functions but how does the df and dg give you lhopital
Because we want to get the limit of f/g
since f=g=0 at the point where they intersect, we use their derivatives to model what will happen right afterwards
aka their derivatives respectively, df and dg
get their quotient
and that lh for you
,rotate ccw
You end up with something like this if f is not equal to g at the point of interest
now the ratio of "dg" and "df" have no meaning, since the increment from f=0 and g=0 is nonzero, meaning f hits zero first, before g
to correctly apply the same process, we would need the two "beams" to start from the same place, where the two functions are equal to zero
All of this requires a comparison to be made from the same starting point
and beyond that, from the same starting point where f=g=0, since starting at any other value (f=g=a) while trivial (lim = 1 duh), would cause l'h to fail, due to the added "increment" that differentiates the intended "limit of derivatives" to be used for l'h and simple limit of derivatives one would try to use for it.
All of this is a bit hand wavy (and way beyond the level of calculus 1). The formal proof uses the mean value theorem IIRC
Try to draw it out. You'll have a sort of "increment" that screws up the dg/df ratio
Wdym
im assuing you mean f=g=1?
I’m lost
Sure
Try to think about it this way
We can get the relative change of f and g when they both equal to 1
But that change is infinitesimal
Compared to the big green box (from y = 0 to 1), whatever difference in their rates of change there is is completely irrelevant
ADDENDUM: This ratio is thus only relevant when there is no big green box (ie. when f=g=0).
It’s ultimately adding an infinitesimal to a number, 1+0.0…2 = 1
Sure, red grows faster than blue, but 1.0000..2/1.0000..1=1 still
In all honesty though, I wouldn’t overthink it unless it’s out of personal interest. The “formal” way of expressing and communicating this is beyond Calculus 1. You’ll get more exposure to it if you end up taking Analysis
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assume there is an isoceles triangle ABC where AB=AC, point E is the midpoint of line AC, and point K is the intersection point of the line that bisects CAB and the circle that touches point A, B, and E, prove that the diameter of the circumcirle is $\frac{4}{3}$ times AK
Skill_Issue
@tall moon Has your question been resolved?
hm
@tall moon Has your question been resolved?
@tall moon Has your question been resolved?
@tall moon Has your question been resolved?
<@&286206848099549185>
@tall moon Has your question been resolved?
Okay, I suppose I have a somewhat computational proof to get some Intuition
You can compute the circumradius of AEB. Let O be the center of this circle. From there, you can compute the angle of the arc AOE and EOK which should give you the angle AOK. You can use this angle and the circumradius to compute AK. Then compare that value to the circumradius of ABC.
@tall moon Has your question been resolved?
how do i compute the arc for aoe and eok tho?
It's double the angle EAK and, AOE you can find using the length of AE
im sorry, i dont know that much about the coorelation between the triangles and their circles, but is arc AOE equal to arc EOK?
if so how?
oh wait nvm
do i use trig for AOE?
arc EK=$\pi r(\frac{EAK}{90})$
arc AE=$\pi r(\frac{sin^{-1}(\frac{AE}{2r})}{90})$
Skill_Issue
Skill_Issue
Skill_Issue
AOK=$4EAK+4sin^{-1}\frac{AE}{2r}$
Skill_Issue
AK=$2r sin(2EAK+2sin^{-1}\frac{AE}{2r})$
Skill_Issue
D: this is absurd why would the olympiad have this question



