#help-38
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got it
I can then just draw a path that adds a circle around the origin
and I'm done
basically this .(dx, dy), and evaluate the line integral clockwise on the unit circle around the origin
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For this Question I am trying to find the equation of the line in the form a+λb, and I have found (the direction ratio for the line) b=-i+2j-k by using the cross product but Im not sure how to find a
hmm
more jee bros
i fucking hated this topic given how boring it was
shocking how many
I hate 3d too 😭
man didn't you have some dumb formula for this
its in a few days so yeah
not really
idk man i can't remember them formulae anyways, is there like a method or smthn
yeah the procedure was to use a random point
snd then you project it to find the smallest distance
ngl this is the most important step
but isn't that for finding the smallest distance, i need the point for my equation
yeah I know
so you assume the point is governed by a parameter t or something
and the random point that you take
the projection of that would coincide with t
oh so basically like (2t+1)-λ=3u+2
and do that for y and z and solve for u or t
yeah I got the answer, thank you very much
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People, how do I find general solution to this ODE? I got as far as dy/dx = (-2yx^3)/(x^4+y^4) but this doesn't seem to be separable
and I don't know what substitution to use here
my notes mention something called "Integration Factor" but I don't know how to apply it here
if it's applicable to begin with
divide the equation by y^4
substitute x/y=t
ok let's see
oh wow, i am not completely stuck anymore
i think i'll figure out the rest myself, thx
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I am happy to help 👴
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In triangle ABC, (b sin C)(b cos C + c cos B) = 42. Compute the area of the triangle.
@pliant thistle Has your question been resolved?
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Hi, I was hoping someone could help me double check my answer for this part c of this question. I think it's correct but I'm not 100% sure to be honest. Thanks!
@zealous sigil Has your question been resolved?
<@&286206848099549185>
it's correct
Thanks so much. I appreciate it.
If it's okay, would you be able to help me with one or two more?
sure
it can be easy to go down the wrong path here
the key is to think about each of the 50 balls independently
for starters, what is the expected value of the first number
So the expected number of times that the sum will be 1275?
Oh wait sorry do you mean the expected value of the number of times a 1 is observed?
That would be 1/20 I think
That's from the previous question
i meant the expected value of the number on the ball drawn
Oh okay
To be perfectly honest I'm sure what it would be
I'm trying to define some variable but I'm not even sure where to start
maybe it helps to scale it down first
suppose you only have two balls, numbered 1 and 2
and you draw one of them at random
what is the expected value of the number you get?
Well I found the probability of getting a 1 first which was 1/2
and the probability of getting a 2 first which was 1/2
and then (1)(1/2)+(2)(1/2)
=1.5
But in this one aren't we continuously taking out 50
In the example you just gave we only choose 1 ball
and that's it
yes
So I thought it would be different
but if you look at the first ball
nothing else has been chosen yet
so it's the same scenario
yeah for now
To be honest I don't
I think there's some formula or something
Oh wait we could take out the 1/1000 constant term and then use that formula
yes
This one
btw, one way to arrive at the formula is to pair up the numbers
1 + 1000 = 1001, 2 + 999 = 1001, 3 + 998 = 1001, etc
but i guess this is not directly relevant to the problem
anyway, we got that the expected value of the first ball is 500.5
Ah that's really clever
now what about the second ball
Well this time I'm not entirely sure to be honest, because I thought about doing this but there aren't 1000 items to choose from anymore
But we don't know which one was picked on the very first one so I'm kind of confused a bit
ok so, the way we calculated it for the first ball is
we found the probability that the ball is each number
which is just 1/1000 for any number
Yeah
so maybe for starters, what is the probability that the second ball is 1?
1/999 right
But hold on, if the first ball picked was actually 1 then it's 0
yeah
I think
Yeah
so how do we combine these to find the probability the first ball is picked on the second turn
I'm so sorry, this sentence doesn't make too much sense to me
no worries
Oh so we want ball 1 to be picked on the second turn
we want P(second ball picked = ball #1)
Then (999/1000)*(1/999) right
yep exactly
Oh what the heck it's just 1/1000
Yeah honestly that's weird
I didn't expect P(first ball is 1) to be equal to P(second ball is 1)
what about P(second ball picked = ball #2)?
Wouldn't that also be 1/1000
yeah
because there's nothing special about ball #1
the same math works for everything else
Yup, I agree with this
so what would be the expected value of the second ball picked
Is it also 500.5?
By any chance
But how would that make sense from the E(X) formula though
Let X2=The ball picked on the second turn
P(X2=1)=P(X2=2)=...=P(X2=1000)=1/1000
But there aren't 1000 balls to choose from anymore right
So E(X2)=Sum(X2*P(X2=x2)) or whatever it is
there aren't
however
I get how the probability is the same
the 999 remaining balls can be any 999 out of the 1000
so there are still 1000 possibilities
But it just doesn't make sense how the expected value is the same
maybe, let's go back to the example with only 2 balls
we have ball #1 and ball #2
either we pick ball #1 first and ball #2 second, or ball #2 first and ball #1 second
so the expected value of the second ball picked is 1/2(1+2) = 1.5
which is the same as the first ball picked
Okay yeah that does make sense
But if you had to do it by defining a variable and then applying the E(X) formula how would you do it?
Or is it not possible to do it like that
Something like this by any chance
what are you referring to by the E(X) formula
The top one
Oh
i presume f(x_i) refers to the probability of x_i?
this is what we're using
1(1/1000) + 2(1/1000) + ... + 1000(1/1000)
Yup
That's for E(X1) where X1 is the first ball picked right
But what about E(X2)
Where X2 is the second ball picked
Yup I agree
But X2 can't take values {1,2,3,4,...,1000} right
Because one ball has already been picked
So you can't sum from 1 to 1000 right
Which is why I'm confused
i guess
it might be better to think about it
as starting before any ball has been picked
we pick 1 ball, throw it away without looking, then pick a second
Okay, so this means we still sum to 1000 then?
Or maybe I'm missing something here
yes
like, the second ball could be any of the 1000
there are 1000 possibilities
here's another way to think about it
generate a random permutation of balls 1-1000
and look at the second ball
(if this is harder to think about don't worry about it but maybe it helps)
Okay yeah this makes sense, we are just looking at all the different ways we could order 1000 balls
this might also help to understand the symmetry
i.e. why all the probabilities are still 1/1000
I get that part
But what's just really confusing me is the values that X2 can take
Like I get the thing that you said about throwing the ball away as soon as it's picked
But I don't know it just feels weird
i guess another way to think about it
instead of drawing from a bag of 999 balls
actually nvm
what i was going to say was
you are drawing from a bag of 1000 "shrodinger's cat" balls
where each exists with probability 999/1000
this might just be more confusing because their existence events aren't independent
Yeah it's dependent right because one influences the other
Or something like that
i think the permutation phrasing probably makes it most clear
any ball could end up in position 2 with equal probability
it doesn't matter what happens in position 1
OHHH WAIT
Because we could have 1 in the second position
We could have 2
We could have 3
Etc. etc. all the way to 1009
1000*
yeah
That's genius okay that makes a lot of sense
Okay that makes complete sense why E(X2)=500.5
I'm guessing they also have an expected value of 500.5 but I'm just going to quickly double check
Yup they're all 500.5
yep
So E(S)=E(X1+X2+...+X50)=E(X1)+E(X2)+...+E(X50)=50*500.5=25025?
Is that maybe how we would do it then?
yes exactly
Absolutely genius man
glad i could help
Just one last thing, it says to compare to when we do replacement
I have a feeling that the expected value doesn't change
Because X1 can take {1,2,3,...,1000}
P(X1=whatever number between 1 and 1000)=1/1000
P(X2=same thing)=1/1000
It's the same thing
yep that's right
Dude thank you so much, you spent so much time explaining that to me. Have an amazing day.
no problem, you too 🙂
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Anyone who can help me understand why this is true, the topic is RSA cryptographics?
are you familiar with euler's theorem?
Yes
so what happens if you take m^(ed)
and then you add or subtract phi(n) from the exponent
ed = 1 mod n ?
i guess i was just explaining why the centered line is true
are you given that ed = 1 mod n here?
no this is for an assignment, i need to explain how RSA works
but i dont understand how to make proof that RSA can be decrypted and output same input
a^phi(n) is congruent to 1 mod n, given that gcd(a, n) = 1
ok right
so you do then have that m is coprime to n, yes?
therefore m^(phi(n)) ≡ 1 (mod n)
yes
therefore you can add or subtract phi(n) to the exponent on m however many times you wish
no, we get m^(ed) ≡ 1 (mod n)
how so?
er
oh my bad, do we?
no, i think i got ahead of myself
i think maybe im missing a bit of context, but can you provide the theorem this is meant to be part of the proof for
i found an assignment that simply stated the text in this picture
but you do have that ed = 1 mod phi(n), no?
well then
do you understand that since $m^{\varphi(n)} \equiv 1 \pmod{n}$ we can also say that $m^{ed} \equiv m^{ed - \varphi(n)} \pmod{n}$?
Ann
this is cause of inverse elements right?
i... wouldn't say so explicitly?
i dont understand this part
ok maybe it would be easier to illustrate my point with some numerical examples
let's consider some stuff mod 10
phi(10) = 4
since 3^4 ≡ 1 (mod 10), we have that for any natural n, 3^n ≡ 3^(n-4) (mod 10)
in other words the exponent can be shifted by multiples of 4 (aka phi(10)) for free
does that make sense to you
yeah so
in the same way in your example we can shift the exponent on m by multiples of phi(n) for free
and this can take us from ed all the way down to the remainder of ed mod phi(n), yes?
✅
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Intuitively, I understand that the triple scalar product gives you the volume of the the parallelepiped. I know that each of the three scalar triple product check if the line is to the left of each of the edges when going trough them counterclockwise. What I dont understand is how to know that the line is on the left or on the right. Note that it also determines which normal of the triangle (front face vs back face) the ray is alinged with. So if going through the triangle in counter clockwise directions you expect the ray to be on the left of all three triangle edges. I just dont understand how the math lets you know whether the ray is on the left of an edge or not. I have attached an image showing the ray-triangle intersection visual and some context.
One more though, if you take A X B and A X B > 0 you know A is on the "left" of B, but nothing here is directly using any edge. all the vectors in any scalar triple product consist of two vectrs from the ray origin to the respective vertices of the edge, and the third is the ray origin going towards the ray direction. So I dont understand how this triple scalar product says if the ray is to the left of the edge or not when we arent directly using the edge.
@scenic lion Has your question been resolved?
@scenic lion Has your question been resolved?
Still trying to parse this myself but here are some thoughts I guess
If we consider
v = [PQ PA PC]
for that particular viewing direction
v = PQ • (PA × PC)
The vector (PA × PC) points into the triangle. I suppose if we think of the plane with normal PA × PC placed against edge AC (AC must in lie in the plane), dotting the normal with PQ would tell us which side point R is on
youre not suppose to put that here
im using this channel lol
please use one of the open ones
Ok im sorry
its okay!
the open ones are under MATH HELP for example like help-15 or help-45 or help-49
why does AC lie in the plane? im imagining a fixed triangle parallel to the xz plane (y going up) and as p goes from being above triangle to below the normal made from PA X PC changes
idk if that makes sense or not
It's like the triangle normal:
You have points P, A, and C. There necessarily exists a plane they all lie in. PA and PC will lie that plane too
PA × PC is normal to the plane
Reading your message now
oh wait i think i see what you mean
This makes sense
Oh btw
I made a visualisation in demsms 3d
Desmos
Which might help
is it okay if i see it
dang that looks good
Thanks
Unfortunately no labels cuz desmos 3d doesn't support them yet
The points are defined at the start
im still trying to understand why you can tell if something is on the left or right of an edge but im going to play around and see if it clicks. either way thanks for doing that and the effort you put into it
It's no problem
I feel left and right are the wrong way to look it tbh
whats a better way to look at it? im open to anything tbh
i just want to understand it better
Since you're comfortable with planes, you may take it as which side the line PQ enters/leaves the edge-plane
Edge plane being the plane containing the edge as described earlier
Or even as whether the vector PQ has a positive component in the direction of normal (this is for the CCW case)
I think the viz should help anyway
Updated viz: https://www.desmos.com/3d/ch8je1sxt5
i understand it from the first visual now thank you, going to look at this one too now
You're welcome 💯
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Working through textbook questions and there are no solutions for this question
I found this proof online but the last part doesn’t make sense to me
If someone could explain or propose a different proof that would help
What app is this?
goodnotes
ight
@lavish cosmos Has your question been resolved?
<@&286206848099549185>
I think it looks okay
Are you meant to write your proof in this list format or is a worded proof sufficient
If the former is true you need to add the axiomatic logic rules at the end of each step to justify what you did
its meant to be a semiformal proof
mainly words with justifications for each line
I Understand that Y is an element of both but why is it neccessarily true that f(D^E) a subset of f(D) ^ F(E)
@lavish cosmos Has your question been resolved?
@lavish cosmos Has your question been resolved?
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so i have trouble trying to simplify this
Suika
I think this is as far we can go
uhhhhhhhhhh
Or did u mean something else?
im trying to see how to get to that expression
the factorisation is a bit confusing 😭
Suika
idek how
Suika
im gonna cry
Suika
this is ur question
multiply the square brackets
yes
ye
from that, we can take 2x common out
and from the rest, we can take (1-4x)³ common out
yes
wait
2x((8x^2(1-4x)^3)+(1-4x)^4)
oh
no wonder why it looked confusing
okay
yayyyyyy
thank you
i lvoe you
and in the remaining part of the terms, there is (1-4x)³ common, that can also be taken out
is that actually the simplest form
oh holy
now what
take it out
wait
we get this after that
let me write it first
wait why 8x^2 when we have 2x out of the bracket
yes
as you can see, there is (1-4x)³ common in the 2 terms
the inside part can be written as -8x * (1-4x)³ + (1-4x) * (1-4x)³
the part inside the [ ]
ok this is where im stuck
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how do i integrate 2/(2x-a)
dont i take the 2 to the left of the integral
Sure
Derivative of?
2x-a
Yup
so this is correct?
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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
if the radicals give you trouble sub n = x^60
yeah i think that's right
,w limit as n goes to infinity (5n^(4/5) - 2n^(2/3))/(2n^(3/4) + 5n)
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looks vaguely correct but i feel like it could be less complicated to begin with.
how
vaguely 
i just put it in like that as i was going by the terms
i got it correct
but how did they simplify it to this
v
16=4^2
yeah the trick is just $\frac{9/4}{1 - x^6 / 4}$ so $\sum_{n = 0}^{\infty} \frac{9}{4} (x^6 / 4)^n$
south
4^(n-1+2)=4^(n+1
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✅
can you show your solution , please ?
well you need to solve it step by step
this
i did
and it is wrong
idk what i did wrong
!showwork
Show your work, and if possible, explain where you are stuck.
not “stuck” but like
yeah
you need to take care when the sum starts from 0 or from 1
in the first line the sum starts from 0
what do i do
you need to take care of the bounds of the sum
how
i did all of this
try it
what is the summing bounds here ?
n=1 to inf
they used n=0 lower bounds probably
I’m just saying the answer is correct if you use n=0
If I followed the standard geometric series approach, This is Definitely a bit different
@late rivet Has your question been resolved?
My solution
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.repoen
what is happening here
sorry
nah its all good
which part
how did we get 1/2 ln (1+x^2)
integration
and why didnt we add C to the left side
cause youre going to set it all equal to y
also
so we only add C to the dx part?
if you added the C to the left side as well they would just cancel out
fuck yeah
u sub
no fucking shit man
anyways
they did u sub
for the x/1+x^2
u = 1+x^2, du = 2xdx
ohhh there is a rule for it
du/2 = xdx
?
do you understand how they got 1/2 ln|1+x^2|
oh yeah
no
they used u-substitution
.
okie
yes
yes
dx = du/2x
now i have (du/2) / (u)
you can pull the 1/2 out
alright
so 1/2int(1/u)
where did the 1 come from
where ?
ohhh
mb
alright thanks
no problem
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how did you get this
well i see it
.open
didnt know that doesnt work
anyway
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@surreal bone
^
the stuff above
?
i couldnt reopen the channel in time
.
no someone took the channel before
anyway if you have a guy ill leave you to it
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Where does the pi come from when the y do fourier ttansform
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The function f(x) = kx + m is given for x ∈ (0,1) and 0 otherwise.
a) What conditions must k and m satisfy for this function to be a probability density function?
Let X be a random variable with density f(x) where now m = -1.
b) Find P(< x <).
c) Compute E(X) and D(-2X).
d) Let Y = 3X - 2. Find the density of the random variable Y.
!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
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can someone please help me with this problem
so im pretty sure youre supposed to use half angle formula for tan
oh wait
yeah just sub and solve the cubic or whatever for cos(x)
Convert cosx to half angle
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Two cars start simultaneously from two reference points A and B at a distance of 500 m, heading towards each other. Car A maintains a constant acceleration of 2.0 m/s2 until it reaches a speed of 20 m/s, continuing in uniform motion (constant speed). Car B always maintains a constant acceleration of 1.0 m/s2.
A. How long after the start do the cars meet?
B. How far from reference point A does the meeting take place?
I haven't been able to solve this problem 😦
what have you tried
It's a bonus for mechanical physics, but I really didn't understand the topic.
do you understand what the question is asking?
I know he asks about mechanical physics and something about the MRU
do you know calculus?
so so
can you write down the position of the 2 cars x(t) and y(t)?
u dont need to apply calc for this qs tbh
theres basic speed formulae u learn in elementary phy but rest is regular algebra
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can you explain in second example its 31 / 33 but it could have been with 26 / 215
can i still do it like 3/6 as 1/2 and do not do first step like he has done what is better?
"can you explain in second example its 3*1/3*3 but it could have been with 2*6/2*15"
wdym?
you mean skip this step?
oh no my bad
Yes
absolutely
how would you do it with 2?
the 9/15, or the 12/30?
i am sorry moonful so my question was incorrect
thats okay
12/30
yes of course, but youll have to simplify it more
try doing it with 2
see what you get
moonful why did they not do it with2
2/5
moonful you think i can improve my math
oh look you got the same answer!!
you can do it with 2, yes, but itll eventually simplify to 2/5 anyway
anyone can
so like there are many ways?
but if i was good at math i could do it like he has done it
in general, though, to do it the fastest, you need to look for the largest number you can cancel
i liked this way of doing
which way?
is this what i was taught at school
what he's doing is just showing how it works
if you can do it directly you're doing great
like in my head when i see a fraction like 24/30 i dont think about this i js go straight to 4/5
no probelm
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How can i find a y vector that is equal to: y = a + c
Hint : Vectors are not static
hear me out
let’s name that point O right
i can’t prove that BO = DC to be able to do anything
the only hint the exercise gives is that ED // AB, DC//FA and FE//BC
Would it be possible if you sent the original question?
yeah hold on
Thank you!
In this case you can prove it (Even if it's more BO = -DC)
hm?
why would BO = -DC
i get that the vectors have different directions
but for now i need to prove that |BO| = |DC|
so i can then say that BO = c
i’m trying to somehow prove that DCBO is a rectangle
it can even work out if it’s a parallelogram
but ive honestly tried everything
It’s so sad that it doesn’t say the diagram is drawn accurately
Have you tried using angles to prove it?
🥲
yeah
i’m trying to utilise that those sides are parallel to play with angles but nothing seems to be working out
Are u french ?
nope
I wish I could be more use but proving stuff with vectors is like a mind game to me
Sorry
Normaly, 'till u r not in university, it is not necessary to say to you that the diagramm is accurate
Do they told u how works Vectors' coordonate
Or vectors' distance ?
hm?
i agree lol
"Coordinates"
well it’d be too much if i used cords
Without it, I don't rly know how to prove it
welp
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Let $e(x)$ be an even function, and let $o(x)$ be an odd function, such that
[e(x) + o(x) = \frac{6}{x + 2} + x^2 + 2^x]for all real numbers $x \neq -2.$ Find $o(1).$
Dork9399
All i know is that an even function implies that f(x) = f(-x) and odd implies -f(x) = f(-x)
did you also know that any function can be broken down into odd and even components like that
atleast continuous ones can
so you know e(1) = e(?)
I suppose that's simpler
(there is a meaningful answer and a cop-out answer to this. i want the former!)
no
the cop out answer would be 1
the cop-out would have been to say e(1)
yes so
e(1) = e(-1)
can you do the same thing for o, but obviously keeping in mind that it's odd
o(1) = -o(-1)
oh lol
yes
ok
now take this: $$e(x) + o(x) = \frac{6}{x + 2} + x^2 + 2^x$$ and put $x=1$.
Ann
don't simplify e(1) + o(1) yet. keep it as it is.
e(1) + o(1) = 2 + 1 + 2 = 5
e(-1) + o(-1) = 6 + 1 + 1/2 = 15/2
oh wait
oh lol
what a solution
x + y = 5, x - y = 15/2
you sure you didnt find e(1) on accident
whoop
i thought i had to separate the function into odd and even components 😭
this is so much simpler
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i put a=b=c=0
then got val of determinant as x^3
so it should be divisible by all right
but answer key is showing only 1 and 2
not like you're meant to be doing it this way anyways lol
why that sub
maybe you could let one parameter be 0 actually
who said!
that sub tells you that you can't rule out x, x^2, x^3
if you got the determinant to be 1 for example, with that sub
then you know the answer is "none of these"
but since you got x^3, it gives you nothing to go on
scamming is an art
sorry i didnt really understand this
maybe with a different sub you get x^3 + x
so it's no longer divisible by x^3
with your sub you know at most it's divisible by x^3, x^2, and x
no it is supposed to be independant of values of a,b,c
not exactly y
otherwise the answer would be subjective
yeah sure
but that doesn't mean that it would hold for your case
that's not how it works
let me give an example
if the answer is x and x^2, x^3 is still divisible by them
"Is 5x divisible by 3"
when someone asks this
it is implicitly for all integers x
clearly if we choose x = 0 it is divisible by 3
compute the determinant normally
algebraically using whichever method you usually do
dude? i would get too many terms
stop being lazy
,w det{{a^2 + x,ab,ac},{ab,b^2+x,bc},{ac,bc,c^2+x}}
sigh
lazy? if this question comes in my exam im supposed to solve it within 2.5 minutes
it shouldnt take you 2 minutes to compute the determinant with some practice
fair
and yeah this time letting one of the parameters be 0 and the other 2 be 1 works
oh ok yeah
why though
again, that doesn't give you certainty
have faith
You only have certainty after a substitution if it turns out its not divisible by x
,w det{{a,-1,0},{ax,a,-1},{ax^2,ax,a}}
@cunning cliff @frozen plover ty guys i got this one right (didnt put a =0 )
i think this is one specific type of problem where u are not allowed to put = 0
cause it worked for most of the others
,w det{{1,3,1},{3,4,1},{2,3,1}}
,w det{{1,9,1},{9,16,1},{4,9,1}}
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ohh
What can you tell me about the sequence?
uhhhhhh
for the first one
6n+9
but
it says 3n
so shouldn't it be
18n squared +9
18n²+9
@wraith hinge Has your question been resolved?
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Plug in 3n in place of n
So 6(3n) + 7
@wraith hinge Still here?
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how do I solve part d? I'm kinda stuck
Consider substituting $u=\frac{x}{2}$
Civil Service Pigeon
i do u sub?

