#help-28
1 messages · Page 270 of 1
wait! i have an unrelated question
how is this incorrect
ive done it several times and gotten the same answer each time
OH
yeah......
first thing that popped out to me 😭
idk guys i MIGHT be bad at paying attention to little details...
lowk same bro
genuinely 😭 up until recently 90% of the points i get off on tests are just like forgetting dumb stuff
thank you for your help kind sirs and madams and whatnot!
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i have my sat in 6 days and im trying to find a desmos explanation on how to do these questions, any help would be appreciated
@feral quest Has your question been resolved?
@feral quest both equations are redundant so we can deal in any one. The question statement asks us to define the line.
What have you tried so far?
ive tried considering r as x and isolating
youd get r=5/7 - 6r/7
but clearly thats not the way to go
consider the first coordinate to be $x$ in each of the points.
This gives you an expression of $x$ in terms of $r$, we good?
yea
now you have to make the second point, which is $y$ in terms of $x$
Adhi
do you see why and how?
yes. If these equations were not redundant, you would use desmos to ||find the common point and consolidate it in terms of the given options||, but since they are, you have to solve the algebra
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!status
What step are you on?
1. I don't know where to begin.
2. I have begun but got stuck midway.
3. I got an answer but I was told that it's wrong.
4. I got an answer and would like my work checked.
5. I have a question about someone else's work/solution.
6. I have completed the problem and don't need help anymore. Thank you.
7. None of the above
But honestly 1
There's a formula for inverse functions and derivatives it's 1/f'(f-1(a))
But I'm not sure how to apply it here
Can you show your work
I don't rly have any work to show
More or less stuck
Yeah
I know that I have to solve for f-1'(2) and that 1/f'(f-1(2)
$(f^{-1})'(x) = \frac{1}{f'(f^{-1}(x))}$
USS-Enterprise
Yes, exactly
First find f(x) = 2
Because we have f^(-1)(2)
There's a 2 that conveniently cancels and just leaves the polynomial expression
But idk how to solve it afterward
$-x^3 + 4x^2 - 7x = 0$
USS-Enterprise
Right?
Yep
USS-Enterprise
We can factor yes
Half correct
When we factor x out, we get
$x \cdot (x^2 - 4x + 7) = 0$
USS-Enterprise
Therefore $x = 0 \lor x^2 - 4x + 7 = 0$
USS-Enterprise
Right
USS-Enterprise
What about the quadratic
I don't think you can factor it without manipulating it
Have you learned the quadratic formula
Ok
You should know if the discriminant > 0, we have 2 real solutions. If it's = 0, we have 1 double real solution. if it's < 0 there are 2 complex solutions
So what's the discriminant for this quadratic
Ok
huh?
Is the b squared minus 4ac the discirminant
USS-Enterprise
USS-Enterprise
USS-Enterprise
-3x^2+8x-7
$f'(x) = -3x^2 + 8x - 7$
USS-Enterprise
-7
USS-Enterprise
$(f^{-1})'(2) = \frac{1}{f'(f^{-1}(2))}$
USS-Enterprise
-1/7
Correct!
Ok that's good it works
Yep
So in summary set f(x) = a then manipulate into something solvable like solving for zeroes then find the derivative of f(x) and use the formula based on the result of the inverse value we calculate
Yes
ok so what if we make it a little harder
like adding a trig function
like if i add tan(pix) to this expression how would solving this change
or if i had e^x or some other things like hyperbolic idk other types of terms
The formula doesn't change
Just how you compute f^(-1)(a), f'
@signal solar Has your question been resolved?
ok
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not sure how to get rid of 12 after plugging in and needing to sovle
there is an easy value x for which f(x)=12
do you know inverse function thoerem
you arent supposed to analytically solve it
no
you can nearly guess the solution
yes
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hi i need help
Using the same reasoning from the previous example:
can you show us said previous example too?
you've waited all of 1-2 minutes and you already yell "ANYONE??? ANYONE HERE???????"
yes
bit impatient of you innit
ok and can you show how they did it in the previous example ie with just one file
are these questions numbered btw
this is their continuation of the previous problem
no
oh ok so they are just part of an infinite string of consciousness.
okay, now tell me this: do you understand what they did in this problem, yes or no.
no
sure is. it's combinatorics.
This channel is only for on-topic discussion. Please take casual conversation to #discussion or #chill.
look, do you wanna help or do you just wanna yap about how hard math is
<@&268886789983436800> troll
girl just get out of this channel please
- there are 30 computers on the network.
- of these computers, 3 particular ones store copies of a file, and the other 27 do not.
- we select RANDOMLY a SUBSET of 5 computers to kill.
- there are C(30,5) ways to select which 5 computers die.
- the file is wiped out if and only if all 3 of the computers storing it are dead.
- for the file to be wiped out, the set of dead computers must consist of all 3 computers storing the file and 2 of the 27 computers not storing the file.
- there are C(27,2) ways to select 2 computers among the ones that don't store the file,
- and therefore there are C(27,2) outcomes in which the file is wiped out.
- finally, the probability of the file being wiped out is C(27,2)/C(30,5).
@torn jolt can you read this and report to me the EARLIEST line number which confuses you?
before you start to read, reply "understood, will begin reading now"
alright
Alright ill read it now
be aware that if e.g. you tell me that line 5 is the one that confuses you then i WILL assume lines 1-4 make sense to you.
line 7-10 confusing
there is no tenth line, what 10th line are you talking about 
there are C(27,2) ways to select 2 computers among the ones that don't store the file,
this is line 7.
there are 27 computers which dont store the file
among these we need to pick 2
C(27,2) ways to do so
if you understood line 4 then you should understand line 7 is the same shit but different numbers
but why are we even doing this
i understand the math behind it but why
yes, 2 computers among the 27 computers that dont store the file
3 machines store the file. 5 machines die.
if file is wiped out, then machines dying = 3 that stored the file + 2 others
alright I don’t get it tbh
okay
lets imagine this
instead of computers on a network there is a bag of balls
30 balls in total
3 red, 27 white
all of them numbered and so pairwise distinct
you pull 5 balls from the bag without replacement
in how many ways could you have all 3 red balls in hand
well
idk tbh
not sure
i know the ways of getting all balls but not specifically the reds
to have all 3 red balls in hand, the 5 balls that you pull have to be those 3 reds and 2 whites
do you understand this, yes or no
yes
ok
indeed
C(27,2)
exactly
thats exactly the same as the amount of selections of RRRWW when pulling 5 balls from the bag
do you understand this, yes or no
no tbh can you explain what you mean exactly
i mean i imagine it as RR
it's not RR...
no
we pull 5 balls and we want to end up with ALL THREE REDS
as i have repeated like several times i think
ok look
lets put more words to it
lets say this is a game of chance
we reach into the bag, pull 5 balls without replacement, and if we catch all 3 red balls, then we win
so with this I selected {WW} ballss
what i am saying is that
each winning selection
is characterized ENTIRELY
by which WHITE balls are in it
if you only had 2 white balls
"had" where.
Then yeah
if you picked
only 2 white balls then the rest would be red
oh is that why
sure if that makes it make sense to you
because i for some reason am not able to explain it to you in a way that sticks
but then you can pick 2 white balls and it can count for if you picked other white balls with it
can you go over why we did this
no obviously i cant
i cant explain it in a way that would make sense to you
i cannot possibly repeat it seven thousand more times and expect it to magically become more clear on the 7001st try
why is it the same though
hey, you try explaining this problem to OP
hrmrmm
alright lets say there are thirty computers numbered from 1 to 30
and say computer numbers 1, 2, 3 are having the file
now 5 computers are chosen out of the thirty
total ways of choosing is 30C5
we need the number of choices where computers 1, 2, 3 are chosen among the five
to ensure the file is completely removed
so three of our choices are already known
indeed
we know that we are going to choose computers 1, 2, and 3
and the other two are the doubtful ones
we could choose those two from the remaining 27 ones
why does this work
numerator shows all possible computer numbers where 1, 2, 3 are present
ohh wait so you have 27 to pick the two remaining ones from
yes
I seeee
1, 2, 3, 4, 5
1, 2, 3, 4, 6
1, 2, 3, 5, 10
1, 2, 3, 7, 9
and so on
as only two of the five which are selected from the remaining 27 vary
its 27C2
welcom
are you done then
for the original problem you can once again assume using numbers
yes thanks bro
yes its the same logic basically
you can close using .close
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Apparently this converges to 0 but idk how
surely the power goes 'faster' than the denomnator, no?
I.e estimate |a_n|
So it should go to infinity
The numerator is oscillating between -1 and 1
Ah lmao
Ok so the denom goes 'faster' to infinity
Which is why its 0
Makes sense
Thanks!
❤️
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Apparently this converges to 1/2
But im confused
If we just ignore the fraction, 1/infinity tends to 0 and sin(0) = 0, so it should be something multiplied by 0 which is just 0, no?
no
you should use $\sin(1/n) \approx 1/n$ instead
south
sin x is around x
So the fraction shouldnt matter?
when x is small
its n^2 in the numerator
Ah yeye
not sure where you are getting 1/inf from
yeah cause you would get infinity * 0
which is an indeterminate form (you can't continue like that)
Ok I see
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In Exercises 101–108, assume that each sequence converges and find its limit.
I thought it would just be like a_n goes to infinity so the answer would be 6/2 = 3, but apparently the answer is 2
I dont see why
How would a_n’s limit be infinity and 3 at the same time anyway
Where did 6/2 even come from
why are you dividing the constants?
It’s better to take n -> infty of both sides in the recursion
Where did 3 come from?
you wrote it?
Why do we want to take it from both sides
You will get an equation with the limit of a_n as an unknown
We get 2 equations, no?
do you agree that lim a_n = lim a_{n + 1}
Or will they both be the same?
Idk I dont really understand this topic
Taking the limits of both sides of an equation yields just one equation
a_n = b_n => lim a_n = lim b_n
$\lim_{n \to \infty} a_n = \lim_{n \to \infty} a_{n + 1}$
knief
I’ll let you take over, knief
😭
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💀
@stuck fiber when the sequence settles down, an+1 and an both approach the same value L
I hope that makes intuitive sense
So just set both equal to L
And solve that equation you get
Ah ok!
I think I get it 😄
Thank you!!
❤️
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you're welcome
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In Exercises 101–108, assume that each sequence converges and find its limit.
I almost got the right answer
I had L + L^(1/2) - 12
I turned that into x^2 + x - 12
So that gives x = 3 and x = -4
Can you just take a picture of your work because that'd be a lot easier
Is sooooo messy 😅
A lot of steps are in my head too
Basically I subbed back in L^(1/2) to get L^(1/2) = 3 and L^(1/2) = -4
So L = 9 and L = 16
Which are both greater than 0
So I didnt know which to pick
In the answer they got the same but they picked 9
I dont understand why?
sqrt is positive, so 12 - sqrt is < 16
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You could also just say 12-sqrt(16) = 8, which is not 16, so it's not a fixed point
12-sqrt(9) = 9, that's a fixed point
L^(1/2) = -4
L = 16
This isn't even right
no square root is ever negative
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guys
With
i asked chat gpt and gauth and they were both wrong
and the video doesnt help
and its due tmr
😔
You know what the area under a velocity time graph represents?
I think the spirit of help channels is to get you to understand it
Not spoonfeed the answers
!noans
The purpose of this server is to help you learn, not to hand out answers. Do not ask someone to give you the answer directly.
knowing this is admittedly paramount to solving the question, and telling them doesn't actually answer the question either, so I believe it's fine
💀
I mean I was gonna tell them what the area under the graph means
But not hand the numerical answer
So think if the velocity time curve was a straight line
Parallel ot x axis
To*
What would area under it be calculated using
What would be the formula
What's the formula for displacement
isnt that physics
Yeah.
Remember velocity is meters per second. So in the. First 250 seconds, it went from 0-14 meters per second at a steady pace. Have you learned how to calculate that?
That doesn't sound right. But if you know how to figure out how many meters it went during the first 250 seconds, the rest should be easy enough.
thats so smart
Id guess it'd be travelling at an average of 7
Because that's half of 14 and it's constant and symmetry stuff
But idk. So for the first 250 seconds, if it's travelling at an average of 7 m/s, how many meters does it go?
?
Did you figure this one out?
it told me to seek help
Ok. This has the same concept
First 250 seconds it seemed to travel at an average of 14 m/s
No it's 7
💔
why do u need to divide by 2
I'm just saying that because it starts at 0 and goes to 14, so it seems average in the middle
Then, for the rest of it, it's at 14
So the first 250 seconds go 1750, but the rest go 3500 per 250 seconds
So 9800-1750=...?
Correct
😎
Now you need to divide that by 14 I think to find how many seconds more
Because it's 14 m/s for the rest
575
So the answer should be 250+575? I think?
I'm not completely sure. Does your homework program tell you if that's correct or not?
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hai, I've been trying to self-study linear algebra for a few months now. I did the same thing with calculus, but at some point, things came "full circle", it kinda feels like im just learning and proving random facts. How do i actually learn this? (sry if thats a bad question)
You probably need a structured curriculum to follow
Either pick out a good book or find a good series online to follow with problem sets
OCW has some nice lin alg lectures I followed. Would recommend!
Also, this is more personal advice, but I'd say try to anchor everything you learn around transformations
Matrices are just the representation of these transformations under a chosen basis, for example
for actual personal interest and genuine desire to grasp, 3blue1brown has a famously helpful visualization series of linear algebra topics that youd find covered in your average one-semester course. very valuable for lin alg in particular IMO because unlike calculus or other math, i feel like without visual aid lin alg is very hard to understand what all the different facets physically represent
it probably wont make you super great at solving problems but if you watch it in junction with something else + problem sets i think its a very valuable supplement
for me at least, determinants were a purely symbolic construct before watching that series, and even though i thought i had a conceptual understanding of how bases work, i realized my understanding was very primitive and watching it helped me get a deeper grasp of both
Beginning the linear algebra series with the basics.
Help fund future projects: https://www.patreon.com/3blue1brown
Music: https://vincerubinetti.bandcamp.com/track/grants-etude
Thanks to Elo Marie Viennot and Ambros Gleixner from HTW Berlin (www.htw-berlin.de) for contributing German translations and dubbing.
Thanks also to these viewers for...
thank you! i think ill just look at a lot of resources and hope to find understanding there. how long does it take to get a solid grasp of the subject?
@gilded bluff Has your question been resolved?
once I really, properly, understood the idea of span and linear (in)dependence, i felt like i could start to put pieces together. a good metric for this is being able to do proofs relating to basis vectors, dimension, span, etc. very easily, or at least being able to tell if theorems are true or false
after that, getting to eigenvalues and orthogonalization was very helpful, because at that point you start to treat matrices as what they are: transformations of n-dimensional space. once you've grasped that, you're pretty much set until abstract algebra
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thank you
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I'm really struggling with this:
I am up to the part where I got to L = sqrt(2) int (from 0 to 1) of 1/(sqrt(2-x^2))
how did u get there
Let me see if I can just upload my tablet writing standby
That is the nice thing about ReMarkable.
Pls forgive how jumbled it is
Is that the trig sub?
yes
well i am abit familiar with trig subs but it comes from the identity sin²(x)+cos²(x)=1
so we can rearrange that as cos²(x)=1-sin²(x)
alternatively, there is a method, where you draw a right triangle and derive its lengths
I wound up trying to keep going until I got to a 1/x situation but ln(0) is undefined and that's where I kept getting stuck. Let me try to run through it with the trig sub
I truly have no idea how I'm supposed to memorize every single one of these trig identities
Ok so I'm almost there.
Just gotta convert the bounds
I'm at sqrt(2) * [arcsin(1/sqrt(2)) - arcsin(0/sqrt(2))]
so it should be sqrt(2) * arcsin(1/sqrt(2))
so you can find the value for alpha maybe easier
so the answer is (pi*sqrt(2))/4
yes
TYSM! I'm all good.
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helo how does this looks like
What do you need help with exactly?
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What have you tried (also ty for not using help 47)
(x,y,z) = (cos(θ), sin(θ), z)
trying to use cylindrical coorsinates
okok
0 <= z <= r
cos(θ) >= |sin(θ)|
r^2 + z^2 <= 4
z ∈ [0, r]
r^2 + r^2 = 4
2r^2 = 4
r^2 = 2
r = sqrt(2)
z ∈ [0, sqrt(2)]
so I found the bounds for the integral wrt z
but I am having trouble finding bounds for the integral wrt theta
this shit is too trig pilled: cos(θ) >= |sin(θ)|
also, we can find the bounds for r I think
x^2 + y^2 + z^2 <= 4
r^2 + z^2 <= 4
geometric intution is a cheat code with these
r^2 < = 4 - z^2
z ∈ [0, sqrt(2)]
is not easy to visualize
a sphere
second
like a ball of radius 4
ya
another ball?
no
help
it's a cone
yeah I guess, yeah
only the positive part of it
not a double cone or anything
you know z^2=x^2+y^2 is pythagoras
so theoretically you have the distance from a point to the origin, and visually a triangle
the z is squared
ya
@leaden ermine
@torpid perch
your point is
r^2 < = 4 - z^2
z ∈ [0, sqrt(2)]
r = 2
r ∈ [sqrt(2), 2]
with the sphere r has interval sqrt(2) <= r <= 2
with the cone... however
0 <= z <= r
oh but we already found z ∈ [0, sqrt2]
this shit is too hard
let me start from scratch
and let me draw a visualization
now we are talking
this is also how inequalities will mean to you something
instead of just being inequalities
u can improve
life sucks
you here @leaden ermine ?
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.i am about to go off anyway, but noticed, you plotted z>=|x| instead x>=|y|
can anyone help me with the question i cant solve it
start with simplifying the diagram by drawing some triangles
ai
now what
i got one that looks like this
that doesn't look like a triangle to me
and one like this
i drew it on paper
ok cool
iont use my computer to draw
so, you've kept the top angles?
Ok, you have these two?
yep
nice, so fill out the lengths and angles
ok
Hint: If you let the plane be O, then you can work out OA from the first triangle and OB from the second.
now what
What do you have for OA?
six eight nine four
that doesn't look right. how did you calculate that?
sin 45 times nine seven fifty
why sin?
opposite over hypotonuse
which is the hypotenuse?
yo iont mean to be rude but can you just show me how to solve it i have like 6 more questions like this and i dont have time like that
i just want to know how to solve these
i did tan 45 and its just the same answer
and this question is supposed to use the sin law
riemann
oooh nice
nope. which sides do you have?
o and h
That's the problem. You should have o and a
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curious
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Might be a stupid question but what does this evaluate to? $\int \sec(x) \left|\sec(x)\right| , \mathrm{d}x$
impract1cal
i mean i guess i can evaluate it case by case? My instinct is that you can just turn this into the integral of sgn(x) sec(x)^2 and i think u can pull sgn(x) out of the integral because its a locally constant function
which then evaluates to sgn(x) tan(x) i guess??
idfk
You can do something like to make it work $\int \sec(x) |\sec(x)| \dd{x} = \frac{\sec(x)}{|\sec(x)|} \int \sec^2(x) \dd{x}$
Azyrashacorki
Then you get a "nicer" expression in the end
Well if anything then you get the antiderivative given by $$\frac{\sec(x)}{|\sec(x)|} \tan(x) + C = \frac{\sin(x) |\cos(x)|}{\cos^2(x)} + C = \frac{\sin(x)}{|\cos(x)|} + C$$
Azyrashacorki
And it turns into that because sec(x)/|sec(x)| is sgn(sec(x))
So you can pull it out
now hold on i stilld ont get how u got this
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I need help with logarithms
For the first 2 images im wondering why we solve for y while the other we dont
And the 3rd image i am confused on what the regular number is to the logarithm. What i mean is when its log 180 or whatever number for that matter what actually is it? Is it the parenthesis so like log(180)? Or what!?
aight hold on
for the first image, is the left hand side meant to be (52/10)^x, or is it meant to be 5*(2^x)?
i mean, for starters there are two different goals here:
in 1 and 2 you want to verify an identity (ie your answer is "yes this is true for all x" or "no this isn't true for all x")
in 3 you are instead solving an equation (ie your answer is a number that, if plugged into x, makes the original equation true)
i am confused on what the regular number is to the logarithm. What i mean is when its log 180 or whatever number for that matter what actually is it? Is it the parenthesis so like log(180)? Or what!?
even after you tried to explain what you mean by "what the regular number is to the logarithm", this is still confusing.
@hoary current Has your question been resolved?
Sorry for the late response
Its the second one
For this i mean when we do the power property its x times log with a number after. However when were writing it the space in between the log and number, what is it? Is it multiplying? Subtracting? Adding? Is there parenthesis?
if it is the second one then the equation is solved incorrectly.
the correct solution would be to first divide both sides by 5 to get 2^x = 36 and then take the binary log on both sides to get x = log_2(36).
log is a function. log(180) is "the logarithm of 180".
people sometimes do not write the parentheses but imo that convention can be & often is misleading.
Wait are you talking about the one thats the same or the one thats not
... i have no idea how to answer that
i guess i am "talking about the one that ISN'T the same"
the 3rd image from your original post
5 * 2^x = 180
this one. i am talking about this equation.
oh, i said "first" and not "third".
rather a big blunder on my part, communication-wise.
my bad.
Ok cus what i thought it was is parenthesis so what you mean is in the formula for logarithms that number is the equals to in exponential form?
christ. that sentence is so damn hard to parse.
Lemme make it easier
When we have log 180
Its log(180)
So
Lets say we were to inverse it so its an exponent
Then that 180 would be equals to the whole other side?
log(180) is the number that answers the question of "10^what = 180"
so i guess i have to answer yes to you, but i sure don't like the way you worded it
Its fine its just i understand it in an exponent way but how would the 3rd image be wrong?
My teacher told us to like put log on both sides of the equation first
Then use the power property then divide by log whatever to get x
$\log(5 \cdot 2^x) \neq x \log(5 \cdot 2)$
Ann
\textbf{if} you were to log both sides of the equation immediately (presumably because the teacher can and will give you zero points as punishment for direct-instruction disobedience), then the correct simplification from $$\log(5 \cdot 2^x) = \log(180)$$ would be $$\log(5) + x \log(2) = \log(180)$$
Ann
mate
i literally asked you
is the left hand side (52/10)^x or is it 5 * (2^x)
you said, and i quote, "the second one"
and now you are revealing to me that you lied to me earlier?
Im sorry i didnt relise you put 5.2 as a fraction😭
i specifically put it as a fraction to make it easier to tell apart from 2^x multiplied by 5 !!!
but this still somehow resulted in a failure of communication.
i ask again for the SECOND time
is it
(5.2)^x
or is it
5(2^x)
tell me once and for all now, WHAT WAS MEANT?
5.2
ok in that case the solution you wrote is correct.
Ok and i have 1 final question
Why is it that we apply log to both sides, and is it multiply by log or put it at the exponent
we do not "multiply by log" nor do we "put it at the exponent".
Are we simply rewriting it?
when we write $\log 180$ or other such things, it \textbf{does not, and never has, and never will} mean the multiplication of 180 by some magical object called ``log''.
as i said before, and as bears repeating, log is a \textbf{function}. we are \textbf{applying} the logarithm function to both sides.
Ann
Why is it that we apply log to both sides
the whole thing of logarithms is that they are the inverse function to exponentials
that's how we get from e.g. 2^x back to x. the function that does this is called the (in this case) binary logarithm, a.k.a. log_2
Ok so your prob gonna get mad at me but when your doing this log thing why arnt we doing the inverse thing where we change the exponent into a log but instead this
a function takes an input and gives an output
if the inputs are the same, then the outputs must be the same
in other words, if a = b then f(a) = f(b)
that goes for any function, including log
if a = b then log(a) = log(b)
what "inverse thing"...
The inverse of an exponent is a log and vyse versa
but you're speaking specifically about some sort of procedure? or what.
Like why are we applying log to both sides? Why arnt we changing the exponent into a log? Is it because when doing inverse its not finding x?
So what your saying is we have an exponent which is x, and we cant find x when its an exponent. So we must change it to a log so x isnt an expoenent. However to do this we must do it to both sides?
where did you get this idea from that you somehow have to "change" something into something before doing the algebraic move appropriate for the problem
this is like if you were saying "When we solve the equation 6x = 24, why aren't we changing the multiplication into a division?"
Because x is an exponent
If x wasnt an exponent we wouldnt need to do this log stuff
So we are using this log stuff to change that x to be do able
So we use that log with the power property to make x not an exponent to solve as normal
not really, i think that's kind of a crooked way to think about things
the relationship between logarithmic and exponential functions
is the same as
between addition and subtraction,
or between multiplication and division,
or (with some wrinkles) between squaring and square-roots.
Ok i understand it for what i need to for now sorry for the trouble but tysm @onyx glen
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hi guys quick question, how to find normal vector given an equation
not ur usual linear equation. but like circle for example
equation of what? a curve in the plane?
and you want the normal to it at a specific point?
that n
I totally get n would be <0,0,1> or <0,0,-1> if it is lying on a the axis plane, but im afraid my prof would be devious enough to ask us this kind of thing
normal to a surface then
yes vyes
is your surface given implicitly or parametrically
parametrically
right ok
then you take the partial derivatives of (x,y,z) wrt u and wrt v, and cross product them
OHH like gradient vector?
gradient would be more visible if you were given an implicit equation ie F(x,y,z)=0
then your normal really would be just grad F
dang ok, so wym by wrt u and v? its 3d
you have a surface defined via 2 parameters right
maybe show the question?
um its not quite a question but ill show u hehe
alr so originally, the circle equation is only x^2 v+ y^2 <= 2
but im just considering other cases where its normal to a surface
ok so your parameters are called r and theta by the looks of it
and how would I find it
yes r, theta, and z
the question just put the circle when z = 0
that why it zero
Go to a free help channel
okay
sooo any idea?
this is a little too disorienting for me to confidently answer with anything
ah ok ok no worries
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help help <@&286206848099549185>
I'm not sure what you're trying to do really. The image above seems to have "3)" which makes me think you've left some details out
thats actually not the point
im just asking how to find this n
Ok. I saw it discussed about it being paramaterised in 2 variables and using the cross product and you understood that.
Is the question about which of the two normals to pick?
nope, im asking given a parametrization of the circle from the pic I drew, how can I find the n
u see, the ones here is just a circle lying on xy-plane
so n is just<0,0,-1>
but im afraid of cases like the picture I dew
drew
Ok I see
Do you know the equation of the circle you drew?
Like it looks like it lies in a plane, maybe z = y?
probably...? hehe not sure its just a thought from my head
If it's z = y you could use a similar trick and say the position vector for all vectors of that plane is r(x, y) = <x, y, y> and use the cross product r_x croxx r_y
so are u saying find two vectors lying on the cirlce with zero dot product and find the cross product of those two?
If the surface lies in a plane you can use this trick is what I'm saying but it always depends on the surface and how it's represented when given to you (it could be given as F(x, y, z) = 0 or x = f(u, v), y = g(u, v), h (u, v) or as z = f(x, y), etc.)
aw dang it, wait lemme try giving u a concrete circle equation that looks like that
Ok 🙂
pls wait, might take a while hehe
No problem 🙂
me experimenting
fahhh i dont think I can find
wait a moment, ill try my last attempt
u know what, z = x^2 + y^2
For a function represented as an implicit function like that which you have no idea what it would look like visually you'd probably use the gradient
gradient vector?
This could be treated as r(x, y) = <x, y, x^2 + y^2> and you can use the cross product trick
I'll try and find a source as you might have come across it before
shouldn't we change x = rcostheta
and the others
You can use any paramaterisation you wish
ahh i see ok ok, and can u tell me what is this cross product trick
i think i forgot
You are essentially finding two vectors on the tangent plane at a point and using the cross product to find a vector perpendicular to them both and therefore obtain a vector parallel to the normal at that point
In this section discuss how the gradient vector can be used to find tangent planes to a much more general function than in the previous section. We will also define the normal line and discuss how the gradient vector can be used to find the equation of the normal line.
ohh I see I see
alr tysm
i think i can close this now
cya
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How can i do this?
surely there's not enough information there
i'm pretty sure there is
guessing this is linear equation in one variable?
you could take speed of river to be x
so when the motor boat moves upstream
it moves against the river and has velocity 20 - x
Yeah
and time = distance/speed
hmyeah
the question when i search it up has an extra "48 km" phrase
Oh
"takes 1 hour more to go 48 km upstream"
Yeahh it had the same for me
Is there some kind of other method exclusively to do this or smth?
hmm i dont think so
O alr then
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How can I calculate the area of this shape?
square minus quarter-circle
I will add by saying that no assumptions are needed, in case you're wondering.
yes, thats what hes talking about
you want the area of the shaded region, correct?
Yeah
that's exactly what you should do.
Yes I tried that and it’s incorrect
please show your working.
divided by 4?
that's not how you factor in the quadrant.
16^2 is indeed the correct area of the square, however. you're just missing a subtraction by the area of that quadrant.
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i got N belongs to {2,3,...,12}
and favourable cases are {4,5,...12}
so shouldnt it be 9/11
yes
Idk HOW it's not in the answer choice
even idk thats why im asking
the question was 4m - 3n
yes
and m and n here, are not exactly the n that you computed. it's kinda misleading but the probability was to be represented in m/n (Or p/q) form, and then you calculate it based on that
m, n is coprime
yes
yes..we represented it in m/n form..
9/11
have you checked what the "probability" of 2 to the power N being smaller than N factorial would be?
Yep
9/11
No way the twin towers is here 💀
yes 😭 we started with that
You see my point?
Lmao
mmmmmm, you might have made a mistake in calculating the 9/11 part
bro laughed at his own joke
Calculate it yourself
what is the mistake..that is what im here to find out
Each sum N doesn't happen equally often. You need to list all ways two dice can add up to a given number. sum = 4 --> 3 ways
Do that for all N and add up
ohhh
Then divide by amount of favorable outcomes
ok let me try
Didn't describe it correctly
i did 1-(P(X=2) + P(X=3) = 1-(1/36+2/36) = 11/12 is this correct?
Yeah
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How do we know that the rocket C is downwards
using the right hand rule?
and j?
