#help-33

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smoky nest
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cyan cove
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how to find minimal solution (minimizing |x|+|y|) for linear diophantine equation (e.g. 17x+19y=524)

cyan cove
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i have general solution to eqn:
x = 542(2)+11n
y= 542(-3)-17n

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i just don't know how to find the n at which |x|+|y| is the lowest

lilac siren
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Well the function |x|+|y| can be separated into at max three intervals since your equations for x and y are linear

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|1084+11n| + |-1626-17n| is what you seek to minimize

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so let's start by looking at the first term

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when is 1084+11n positive and when is it negative?

cyan cove
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when n < 1084/11 its negative

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i mena

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n < -1084/11

lilac siren
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ys

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and now what about the other term

cyan cove
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and positive when greater

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and for the other when n < -1626/17 its positive

lilac siren
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exactly let me briefly calc which one is lower

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-1626/17 is lower k

cyan cove
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yeah

lilac siren
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so you have three cases:

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-X-Y if n<-1626/17
-X+Y if n<-1084/11
X+Y else

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if you find the minimum of these three you found the total minimum

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shall we do the first one together

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or do you prefer to attempt yourself

cyan cove
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hmm

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i feel like i've done smthn wrong

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wait nvm i havent

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im getting the total minimum = -1626/17

lilac siren
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do you mean at n = -1626/17

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or the value of the minimum

cyan cove
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yeah

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at n = -1626/17

lilac siren
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yop

cyan cove
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like first derivative test

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i probably didnt have to do that

lilac siren
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you don't need to

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Its linear

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which means the minimum of each interval

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is one of the two boundary values

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the minimum of a linear function on the interval [a,b] is either at a or b

cyan cove
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true

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wait i feel like i fucked this up tho

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if i plug in -96

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to my general solution it doesnt work ๐Ÿ’€

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maybe my general solution is wrong 1 sec lol

lilac siren
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ok what was the initial question

cyan cove
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o no it works

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nvm

lilac siren
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kk

cyan cove
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wait

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nvm ๐Ÿ’€

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i forgot to specify the problem correctly

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so y has to be <= 0

lilac siren
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What was the initial question :D

cyan cove
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nvm i got it

lilac siren
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๐Ÿ˜„

marsh citrusBOT
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@cyan cove Has your question been resolved?

marsh citrusBOT
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minor rivet
marsh citrusBOT
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lucid trail
marsh citrusBOT
lucid trail
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Does this seem to be right?

steel sluice
lucid trail
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oh thank you

marsh citrusBOT
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@lucid trail Has your question been resolved?

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quaint crescent
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Can somebody explain to me what the "0 rule" is? I just don't get it...

quaint crescent
quiet anvil
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@quaint crescent is the "0 rule" the rule they used to break this up into cases?

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x = 0 or x+3 = 0

quaint crescent
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Yeah

quiet anvil
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Ok

quaint crescent
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I translated it literally

quiet anvil
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Let's say you have two numbers

quaint crescent
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5 and 7

quiet anvil
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Let's call them y and z

quaint crescent
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Okay

quiet anvil
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And you know that y times z = 0

quaint crescent
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How

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One must be zero then right

quiet anvil
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Let's just say that you arrived at this expression from something unrelated.

quaint crescent
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Either z or y

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Okay

quiet anvil
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Or both

quaint crescent
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Right

quiet anvil
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But what about neither?

quaint crescent
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Then it wouldn't be possible

quiet anvil
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Correct

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So either y or z (or both) must be 0

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Now let y = x and z = (x+3)

quaint crescent
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But with what logic does one cut apart x(x+3) into 2 seperate terms

quiet anvil
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Well yz = 0 implies y or z is zero. That is exactly y = 0 or z = 0.

quaint crescent
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Doesn't it imply that y*z is 0

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So why is the multiplication thrown out and forgotten

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There's some background stuff left untold or otherwise im just stupid

quiet anvil
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Well, I think you might have a rather rigid understanding of math manipulations, so it's understandable that this might make you uncomfortable. So let's approach it a different way.

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You have x(x+3) = 0

Divide both sides by (x+3), we are asserting x+3 โ‰  0 by doing this.

x = 0/(x+3) = 0.

We can verify that 0+3 โ‰  0.

What about the case where x+3 = 0? Well in that case we have x(x+3) = x(0) = 0. Which from the original expression is a true statement. So x+3 = 0 is also valid.

quaint crescent
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What....?

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Im kind of an idiot so...

quiet anvil
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You are not. Learning is hard

quaint crescent
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0+3โ‰ 0 yes

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But where does 0+3 even come from I'm kinda lost

quiet anvil
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We asserted that x+3 โ‰  0. Using this assertion, we found x = 0. Now we must check that our assertion was not violated by substituting in the result into the assertion.

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That's how we got x + 3 becomes 0 + 3.

quaint crescent
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Okay...

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So when I see an expression where i have factored something

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I can just take both of the terms and separate them

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And make them equal 0

quiet anvil
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Yes.

quaint crescent
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Does the x+3=0 continue by turning into x=-3?

quiet anvil
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Yup!

quaint crescent
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Okay

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Thanks :)

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ใ‚ใ‚ŠใŒใจใ†๏ผ

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marsh citrusBOT
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safe sparrow
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how do I work through these?

marsh citrusBOT
bold ice
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You have 2 points

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of the tangent line

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(0,0) and (b, f(b))

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From that you can find the inclination

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that is equal to f'(b)

safe sparrow
bold ice
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yeah

safe sparrow
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how might I go about doing question 4b?

bold ice
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same process

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the derivative wont have k

marsh citrusBOT
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@safe sparrow Has your question been resolved?

safe sparrow
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got the first one, working on the second

safe sparrow
# bold ice the derivative wont have k

if the derivative doesnt have k, how can i put k in terms of b using the following info?

so far ive worked out that the tangent line is y=x*2e^(2b)
and thus b = 1/2

bold ice
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The tangent line has k in it

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m = (f(b) - 0)/(b-0) = f'(b)

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So e^{2b+1}+k = b*f'(b)

safe sparrow
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ive got it now

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thanks for the help @bold ice

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calm harbor
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Completely 0?

marsh citrusBOT
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@still temple Has your question been resolved?

still temple
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ebon depot
marsh citrusBOT
ebon depot
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X is unknown matrix.
Determine X if we know XA = XC+B

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Hint: Transpose and Gauss Elimination are your friend

marsh citrusBOT
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@ebon depot Has your question been resolved?

marsh citrusBOT
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@ebon depot Has your question been resolved?

frail orbit
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@ebon depot

ebon depot
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XA - XC = B
X(A-C) = B

frail orbit
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this tells you what the dimensions of X must be

ebon depot
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So the dimensions of X multiplied with (A-C) which is a 2x3 should result in a 2x3 matrix?

frail orbit
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yes

ebon depot
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So X is a 3x3 matrix?

frail orbit
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no..

ebon depot
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sorry

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meant 2x2 matrix

frail orbit
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yes

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now you can either right multiply both sides by B^T or right multiply by (A-C)^T

ebon depot
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I'm not sure what you mean

frail orbit
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B^T=B transpose

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AC is right multiplying A by C

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so basically either X(A-C)B^T=BB^T or X(A-C)(A-C)^T=B(A-C)^T

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now note the dimension of (A-C)B^T and (A-C)(A-C)^T in either case

ebon depot
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But i'm trying to solve for X?

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thank

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FUCKKKKKKK chart is here

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i've been trying to get help since 12 pm

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7 hours and 42 minutes later ;-;

glass silo
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Awww sadcat

glass silo
glass silo
ebon depot
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I'm not sure why we would want to transpose

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X(A-C) = B

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This is what i have?

glass silo
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Sure, but if you multiply by one of those transposes, the answer to the previous question will give you a hint of what you can do catThink

novel juniper
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one way of doing this, though that would be rather ugly, is to assume a general matrix X and then compute (A-C) and solve, but I wouldn't recommend that

glass silo
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@astral trout Hiii

astral trout
novel juniper
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calm down

ebon depot
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no

glass silo
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What type of matrices are your favourite? catThink

ebon depot
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I just want to understand

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what i am doing

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and how to solve it

glass silo
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Alright, say I gave you instead something like
[
\pmqty{2 & 1 \ 0 & 5} X = \pmqty{1 & 2 \ 3 & 4}
]
Would you know how to find $X$ in that case, or have any ideas?

elfin berryBOT
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@glass silo

ebon depot
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Yes

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Multiply both sides with the inverse of 2105

glass silo
ebon depot
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But we multiply with the inverse on my question

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because it's a 2x2

glass silo
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Sure, or because it's square OathLove

ebon depot
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yea

glass silo
ebon depot
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(A-C) = 2x3
B^T = 3x2

glass silo
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So then if you multiply them together, you get...? catGiggle

ebon depot
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2x3

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2x3*3x2 = 2x2

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mb

glass silo
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Ooohhh, a square matrix happyCat

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So it might be invertible catThink

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If it is, we can just multiply by its inverse to get X by itself Foxy_Popcorn

ebon depot
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$X(A-C)B^T = BB^T$

elfin berryBOT
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Merineth

ebon depot
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since (A-C)B^T = 2x2 matrix?

glass silo
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Yea, that's a 2x2 matrix (as per above, it might be invertible, though of course it's worth making sure that it is - being square is necessary but not sufficient for being invertible!)

ebon depot
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So now i calculate (A-C)B^T and BB^T

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?

glass silo
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Yea, pain sadcat

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Not the worst in the world but still monke

ebon depot
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How does it become a 2x2 ?

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oh nvm

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Just tired

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37 47
19 29

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(A-C)B^T

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and

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182 22
22 62
BB^T

glass silo
glass silo
ebon depot
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for sure

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the calculation will be insane?

glass silo
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catThink annoying a bit monke but doable

ebon depot
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37 47 | 1 0
19 29 | 0 1

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Don't i just divide by 37 on the top and 29 on the bottom to get 1:s instead of 37 and 29

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and then i add with a mutliple of something to get 0 on 48 and 19

glass silo
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You could do it like that, but for 2x2 matrices, their inverses are quite easy to find

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The inverse of $\pmqty{a & b \ c & d}$ when it is invertible is $\frac1{ad - bc}\pmqty{d & -b \ -c & a}$

elfin berryBOT
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@glass silo

ebon depot
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ah right forgot

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Okay there we go

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that seems to be right?

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inverted it to get it to the RHS
then did matrix multiplication

novel juniper
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this is another question ?

ebon depot
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Yes

novel juniper
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so you have to find X is AX=3X?

ebon depot
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"Determine all the vectors $X_{3x1} for which AX=3x if A = ... "$

elfin berryBOT
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Merineth

ebon depot
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This is what i did on it

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I can't figure out any other way it could've been solved

novel juniper
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just a suggestion use \text{ the text }to enclose text when you're typing latex in the future

glass silo
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More that put the dollars only around the math

ebon depot
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Yeah i know :( I've been at it for 8 hours and 40 minutes now and i'm on question 3 so i'm kinda lazy about latex atm

novel juniper
ebon depot
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thank GOD

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3 more monkey

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Hang in there mee!

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do a inverse of an inverse cancel each other?

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For example

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I want to solve for A

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Do i just take the inverse on both sides to remove the inverse on the LHS?

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or sorry

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I just remembered

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If i multiply both sides with (A-6I) then LHS cancels out

ebon depot
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Help me :c

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Can i do this

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$(A-6i)^{-1} = M \
M(A-6i) = I \
MA - M6i = I \
MA = M6i + I \
A = 6i+I$

glass silo
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Is M supposed to be the matrix on the left, this one?

ebon depot
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yes

glass silo
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And if so, no SCsadkittyNO

ebon depot
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why

glass silo
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The right would be the identity matrix if you're doing it like that instead though, if you wanted

glass silo
# ebon depot why

Multiplying an invertible matrix with its inverse gets you the (multiplicative) identity, not zero

ebon depot
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i just get the identity matrix not zero?

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But why can't i do it like i did?

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and instead of zero

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i make it I (identity matrix)

elfin berryBOT
#

Merineth

astral trout
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@glass silo
what about this? expand the brackets and move over -6I or is this illegal too

glass silo
glass silo
ebon depot
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A = 7i?

glass silo
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Not quite no SCsadkittyNO (also better to have all the small i's as capital I's, to represent the identity matrix)

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What you would have, if M was invertible (it better be!) is A = 6I + M^{-1}

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(multiply from the left by M^{-1})

ebon depot
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what about it is wrong thjen :c

glass silo
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Explain what your thoughts are to get from the second last line to the last one?

astral trout
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no latex sorry i got beat up by c++ today

glass silo
elfin berryBOT
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@glass silo

glass silo
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Oh wait also hmmCat with that said...

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Actually anyways

glass silo
# elfin berry **Merineth**

From $MA = M(6I) + I$, multiply on the left by $M^{-1}$ (as before it better be invertible!) to get $A = M^{-1} ( M(6I) + I )$

elfin berryBOT
#

@glass silo

glass silo
#

Expanding that out gets you $A = 6I + M^{-1}$

elfin berryBOT
#

@glass silo

glass silo
#

You can also notice that by inverting both sides of $(A - 6I)^{-1} = M$ to get $A - 6I = M^{-1}$ and $A = 6I + M^{-1}$

elfin berryBOT
#

@glass silo

astral trout
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and we can solve for A if and only if M has an inverse basically

astral trout
#

so if ur allowed to just invert the expression on lhs and do the same on rhs i feel like that would be the easiest?? if thats legal

glass silo
ebon depot
#

$M^{-1}MA = M^{-1}M6I$

elfin berryBOT
#

Merineth

glass silo
ebon depot
#

I am?

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$MA = M6I$

elfin berryBOT
#

Merineth

ebon depot
#

this is right?

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huh

glass silo
ebon depot
#

$(A-6I)^{-1} = M \
M(A-6I) = I \
MA - M6I = I \
MA = M6I + I$

#

My initial thought was that i want to "move" M to the RHS

glass silo
#

Capital I, not small i OathLove

elfin berryBOT
#

Merineth

ebon depot
#

So now finally i want to "move" M to the RHS so i solve for A

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and to move a matrix

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i need to multiply it by it's inverse, right?

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So

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$M^{-1}MA=M^{-1}M6I+I$

elfin berryBOT
#

Merineth

ebon depot
#

$IA = I6I+I$

elfin berryBOT
#

Merineth

ebon depot
#

WHAT

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how is that wrong

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i'm multiplying both sides with

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M^{-1}

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oh..

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HAHAH

#

okay hold on

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$M^{-1}MA = M^{-1}(M6I+I)$

elfin berryBOT
#

Merineth

ebon depot
#

$IA = M^{-1}M6I + M^{-1}I$

elfin berryBOT
#

Merineth

ebon depot
#

Can LHS be written as A?

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$A = I6I+ M^{-1}I$

elfin berryBOT
#

Merineth

ebon depot
#

(caps lock wasn't on :c)

#

Isn't I^2 = I?

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$A = 6I + M^{-1}I$

elfin berryBOT
#

Merineth

ebon depot
#

Don't you dare leave chartbit <3

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got 2 more ;-;

#

just calculating the matrix for A

frail orbit
#

lmao

ebon depot
#

me holding chartbit hostage for math questions

#

What does it mean when a matrix is perpendicular and symmetrical?

frail orbit
#

orthogonal?

ebon depot
frail orbit
#

orthogonal matrix means its columns dot products are all 0

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the columns form an orthogonal basis

ebon depot
#

I'm supposed to determine B^{-1} to

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$B= 21A^{105}+79A$

elfin berryBOT
#

Merineth

frail orbit
#

orthogonal matrices have a nice property

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symmetric matrices also have a nice property

frail orbit
# ebon depot

so this is saying A is an orthogonal and symmetric matrix?

ebon depot
#

Yes

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And that it is a 19x19 matrix

frail orbit
#

A is symmetric implies that A=A^T

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A is orthogonal implies that A^T=A^-1

ebon depot
#

Doesn't that just mean that

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$A = A^T = A ^{-1}$

elfin berryBOT
#

Merineth

frail orbit
#

so A is its own inverse...interesting...

#

what does that tell you about $A^{2}$

elfin berryBOT
#

MSC2020 55N31 (Moosey)

frail orbit
#

@ebon depot

ebon depot
#

I'm not sure

frail orbit
#

$A^{2}=AA$

elfin berryBOT
#

MSC2020 55N31 (Moosey)

ebon depot
#

Yea

frail orbit
#

and if A is its own inverse...

#

what is AA

ebon depot
frail orbit
#

A=A^-1

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so you can sub in A^-1 for one of the As, yes?

ebon depot
#

OOOh

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so

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$A^2 = AA = AA^{-1}$

frail orbit
#

no...

elfin berryBOT
#

Merineth

frail orbit
#

yes

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and AA^-1 is...

ebon depot
#

I

frail orbit
#

mhm!

#

so note you have a power between even power and odd power of A

ebon depot
#

The odd power makes it 21A ?

frail orbit
#

A, A^2=I, A^3=(A^2)A...

frail orbit
ebon depot
#

$21AI^{104}$ ?

elfin berryBOT
#

Merineth

frail orbit
#

well, technically I^(52)

ebon depot
#

ah right

frail orbit
#

but still right

#

so now you can just apply inverse properties to find the inverse of B in terms of A

ebon depot
#

so essentially

#

$B = 21A+79A$

elfin berryBOT
#

Merineth

ebon depot
#

$B = 100A$

elfin berryBOT
#

Merineth

frail orbit
ebon depot
#

So now we just want the inverse of 100A?

frail orbit
#

ye

ebon depot
#

$B^{-1} = 100A^{-1}$

elfin berryBOT
#

Merineth

ebon depot
#

Is this allowed?

frail orbit
ebon depot
#

so we take the inverse of both 100 and A?

#

$B^{-1} = 100^{-1}A^{-1}$

elfin berryBOT
#

Merineth

ebon depot
#

Based on property 2

frail orbit
#

yes

#

100^(-1)=1/100

ebon depot
#

Nice

#

And since we aren't given the A matrix

#

i believe we are done?

#

Last one for today

#

and it's diiiiiiiiiiiiiiiisgusting

#

(The old man in the drawer) A cubic drawer has a corner at the origin and edges OA, OB and OC with other points in the points A = (2,โˆ’2, 1), B = (1, 2, 2) and C = (โˆ’2,โˆ’1, 2). A dot-shaped old man is at the point with coordinates (0.9,โˆ’0.9, 4.5). Is the old man in the drawer? Tip: Transfer to a suitable new base. Rephrase the question 'lie in the drawer' i algebraic terms. What finesse does the change to a new ON base offer?

still temple
#

if the point isnt as far away as B in the B direction, not as far away as C in the C direction and not as far away as A in the A direction then its in the cube

ebon depot
#

@glass silo ;-;

#

comeback

#

.close

marsh citrusBOT
#
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marsh citrusBOT
#
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azure trench
marsh citrusBOT
azure trench
#

Question is: find all 2x2 matrices A, with real entries such that A^2 = -I where I is identity matrix

azure trench
#

Oh the circled things are my answers

#

Im just wondering how youโ€™d know how many different combinations there are as well

#

Ohhh I should have assumed bc = 0

frosty linden
#

So what are the form of the matrices ? Sry I didn't see the answer

azure trench
#

What do u mean by form

frosty linden
#

If AD=0 we can't have bc=0

azure trench
#

There is no AD, is there?

frosty linden
#

What are the matrices A such that Aยฒ = -I

#

The product ad

#

Because you Say a=0 and d=0

#

So the product is 0

azure trench
#

Yeah but if the product isnโ€™t in the matrix why is it relevant

#

Iโ€™m not doubting u im just lost

frosty linden
#

Yes sure but we know that A is invertible so his determinant is non zero so with ad=0 we already know that bc is not 0

azure trench
#

Ohhhh determinant didnโ€™t cross my mind for this

#

Fair enough

#

Ohnshit yeah

frosty linden
#

I don't read all the calculation but if you did that correctly it seems to be the good reasonning

azure trench
#

Oh yeah I said bc = -1

#

To make it into identity matrix

#

Okay I donโ€™t think this is wrong

#

But thereโ€™s so many more answers ffs

frosty linden
#

๐Ÿ‘

azure trench
#

Okay thanks

#

.close

marsh citrusBOT
#
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hasty lotus
#

quick SUVAT question

marsh citrusBOT
hasty lotus
#

I have confirmed question a to be 1.22s to its max height then that will also be the same for time taken to reach starting point

brittle coral
frozen delta
#

that is correct

hasty lotus
#

with part b would it be -1.5 x 1.22s or would it be for the full 2.44s

brittle coral
#

full 2.44

hasty lotus
#

okay so -3.66m to the left of original position

#

thanks all

#

.close

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vocal cloud
#

can i please get help with this

marsh citrusBOT
vocal cloud
#

i dont exactly see how they are going from first line to second

harsh falcon
#

think about it visually

#

im gonna draw something

vocal cloud
#

but like if i were to show it mathematically

harsh falcon
twilit arrow
#

if A and B are disjoint, then P(A) + P(B) = P(A U B)

#

A and A' are disjoint

#

and so A n B and A' n B are as well

#

from there it's just undoing distributivity

vocal cloud
twilit arrow
#

yes

#

the inside is equivalent to the inside in the original pic

#

it is undoing distributivity

vocal cloud
twilit arrow
#

(P n Q) u R = (P n R) u (Q n R)

vocal cloud
twilit arrow
#

no

#

im saying undoit

vocal cloud
#

oh

twilit arrow
twilit arrow
#

identify P, Q, and R

#

then plug them into the left hand side

vocal cloud
#

oh

#

got it

#

thankyouu so much

#

.close

marsh citrusBOT
#
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dawn elbow
#

I neeed help again

marsh citrusBOT
dawn elbow
glad kernel
dawn elbow
#

im confused here on what he did with the bounds to turn them into 2 and 0

#

from 20 and 16

hazy lion
#

so, you either need to switch the bounds or keep track of the old variable

left wadi
#

when you do a sub the bounds change

hazy lion
#

since the sub is u=x-16 here

#

the 16 becomes 16-16=0

dawn elbow
#

but its root x-16

hazy lion
#

20 should be 20-16=4 KEK

#

not 2

#

but whos counting

left wadi
#

@hazy lion you forgot to root

#

sqrt(20-16)

#

is 2

hazy lion
#

oh, youre right

dawn elbow
#

so if there are bounds and i have to do u sub then i need to plug in the bounds to the u sub formulas to see what they changed to?

left wadi
#

yes

hazy lion
#

and undo the substitution on the back end

dawn elbow
#

where did he get u=0 from

hazy lion
#

if you convert the bounds, you dont have to undo the substitution

hasty lotus
hazy lion
#

if you dont convert the bounds, you do

#

so you just have to decide which one is less work

dawn elbow
#

where did he get u=0 from?

left wadi
#

on the right side?

dawn elbow
#

oh oh nvm u^2=16-16

#

okay ty

left wadi
#

sqrt(16-16) = 0 yeah

dawn elbow
#

so the upper bound becomes ur new x and ur lower bound becomes ur new U?

#

like why did he chose to sub in x=20 at the start and then u=16

#

did he mean if x=16 u = 0?

left wadi
dawn elbow
#

i have

#

another question

#

how come B is just B and not Bx+c

marsh citrusBOT
#

@dawn elbow Has your question been resolved?

#
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young swan
#

Can anyone check if I've calculated this correctly? I guess this is physics but it seems appropriate to ask here

young swan
#

please ping on reply, will be heading off to bed ๐Ÿ™โค๏ธ

graceful owl
#

So equivalent resistance is (20R)/(20+R) + 11

graceful owl
#

Then solve for R

#

@young swan

young swan
#

oh god wait is my shit wrong

#

So this ain't enough to just get the resistance for R ๐Ÿ˜ญ?

#

That's a shame cause that is one beast of an algebraic question idk if i got the patience for

graceful owl
#

R in ohms law isnt 11

#

Itโ€™s 11+the parallel eqn of 20 and R

young swan
#

well, I was gonna head off but I kinda wanna solve this first.

#

2am math time? skull

#

but btw will this work?

#

0.35A isn't like

young swan
#

It's just through 20 Ohm resistor

graceful owl
#

Ohh wait im being dumb the amperage is out of the 20ohm

#

Not the whole circuit

#

Sorry im also really tired

young swan
#

It's alright this is one of three servers I've asked in, so even if one strikes out it's ok by me

#

You should head to bed if possible

#

I have 8 hours before i need an answer, bcs that's when my exam is. I'll be heading off to bed

#

AS YOU SHOULD !!!

#

โ—

#

I'll be heading off legit rn, so once again, if anyone do reply, please ping ! โค๏ธ

marsh citrusBOT
#

@young swan Has your question been resolved?

marsh citrusBOT
#
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#
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spring stirrup
#

how did they get -1539 ?

#

I plugged in 2 and i keep getting random numbers

marsh citrusBOT
#

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plucky blaze
marsh citrusBOT
plucky blaze
#

im understanding it cant be D and E because those would hacve the same magnitude

#

and i think its not A because the charges cancel from both things

#

and then my multiple choice brain gives me the answer B but it could be C and idk why it would be B

#

i think it would be B and not C cuz its closer to any charge

#

but if there was just an E and not a D i wouldnt know if it was B or E

#

and the second one im fully confused what its saying

marsh citrusBOT
#

@plucky blaze Has your question been resolved?

plucky blaze
#

i think the 2nd one is A actually now bc there should be no force on that one itshoudl all cnacel out

marsh citrusBOT
#

@plucky blaze Has your question been resolved?

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lilac siren
marsh citrusBOT
still temple
#

find f^-1(2)

#

you dont need f^-1(x)

lilac siren
still temple
#

why 2ยฒ

hushed egret
# lilac siren

are you one of those people that write R^+ for [0, infinity)?

lilac siren
#

since f(x) = sqrt(2 + x + x^4)

still temple
#

oh yeah right

still temple
#

Well you can get x=1

#

pretty easily

hushed egret
#

wait nvm lol

lilac siren
still temple
#

can you get f'(x)

lilac siren
#

nup

still temple
#

what

lilac siren
#

idk how to get f'(x)

#

ah sry f'

#

ofc

still temple
#

can you find f'(1)

lilac siren
lilac siren
#

without guessing

#

eg if the task were instead:

#

I'd have 5ยฒ = 2 + x + x^4

still temple
#

calculator i guess

lilac siren
#

oh so there's no direct approach?

still temple
#

but once you get x

lilac siren
#

aw that's boring

#

k thank thee then :)

#

.close

marsh citrusBOT
#
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lilac siren
#

was the closure timer increased?

marsh citrusBOT
#
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rough trellis
#

dibs

marsh citrusBOT
rough trellis
#

what is m<EDC

#

i have no idea what to do

civic moss
marsh citrusBOT
#

@rough trellis Has your question been resolved?

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#
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rigid breach
#

Does anyone know to formula for question 11 b

dry prawn
#

the maximum value of a parabola occurs at its vertex

#

do you know how to find that?

marsh citrusBOT
#

@rigid breach Has your question been resolved?

rigid breach
#

I donโ€™t even know what a vertex is haha

#

Oh ok highest point

#

But idk how to find that

#

I think thereโ€™s a formula but I completely forgot

dry prawn
#

you don't know what the vertext form is?

rigid breach
#

Nope

dry prawn
#

y = a(x-h)^2 + k

#

not ringing any bells?

rigid breach
#

That reminds me of completing the square

#

Of a quadratic

#

But idk how itโ€™ll help in this case

dry prawn
#

it helps because the vertex is precisely (h, k)

#

that's why it's called vertex form

rigid breach
#

OHHHH

#

I didnโ€™t know that this form was equal to that

#

And so

#

Is h =x and k=y

dry prawn
#

what?

rigid breach
#

U said the vertex is h and k right?

#

So like, what do I do with them to get my answer

#

Cuz the answer is 159m

dry prawn
#

(h, k) is an ordered pair like (x, y) if that's what you're asking

rigid breach
#

Yaaa

#

Ok thank you

marsh citrusBOT
#

@rigid breach Has your question been resolved?

rigid breach
#

.close

marsh citrusBOT
#
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#
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ebon depot
marsh citrusBOT
ebon depot
#

(The old man in the box) A cubic box has a corner at the origin and edges OA, OB
and OC with others in the points A = (2, โˆ’2, 1), B = (1, 2, 2) and C =
(โˆ’2, โˆ’1, 2). A dot-shaped old man is at the point with coordinates
(0.9, โˆ’0.9, 4.5). Is the old man in the drawer?
Tip: Transfer to a suitable new base. Rephrase the question 'lie in the drawer' in ยจ
algebraic terms. What finesse does the change to a new ON base offer?

#

I assume i want to make a base with OA, OB and OC?

sand fable
#

(somewhat interesting how a different person posted this exact problem 2 days ago)

ebon depot
#

It's probably because we go to the same school and we aren't getting any help from the teachers on these questions

sand fable
#

makes sense

sand fable
ebon depot
#

transform?

#

@glass silo Sleeping? ;-;

#

<@&286206848099549185>

marsh citrusBOT
#

@ebon depot Has your question been resolved?

ebon depot
#

Anyone?

#

I found a similar answer online but i dont' know how to interpret it

#

dead discord ๐Ÿ˜”

#

.close

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#
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steel sluice
#

what is this function

marsh citrusBOT
fathom hornet
#

hii, im a grade 6 student and i need help with percentages convertion since its our test tomorrow, is tutoring allowed here? to be specific, I need help with decimal-fraction & vice versa, also fraction to percent. thanku!

drowsy gust
#

!occupied

marsh citrusBOT
#

Someone else is already using this help channel. If you need help with a question, please open your own help channel/thread (see #โ“how-to-get-help for instructions).

drowsy gust
#

$\mod(x,y) = x \mod y$

elfin berryBOT
#

AlphaNull

steel sluice
#

thanks

#

.close

marsh citrusBOT
#
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fathom hornet
#

hii, im a grade 6 student and i need help with percentages convertion since its our test tomorrow, is tutoring allowed here? to be specific, I need help with decimal-fraction & vice versa, also fraction to percent. thanku!

steel sluice
fathom hornet
#

how?

fathom hornet
#

oh, thanks

marsh citrusBOT
#
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dense lynx
#

hello for this question, I always seem to get only on epossible answer for a and b (3 and 18)

drowsy gust
#

i assume you plugged in a + ai into x^2 - 6x + b

#

you should have gotten $b = 6 a - 2 i (-3 a + a^2)$

elfin berryBOT
#

AlphaNull

drowsy gust
#

and using the fact that b must be real, its imaginary component must be 0

#

and the imaginary component on the RHS is a quadratic which has two solutions

dense lynx
#

i used the sum and product of roots rule

#

so we know the two roots are a-2i and a+2i so

#

a-2i+a+2i = 2a (sum)

#

(a-2i)(a+2i) = 2a^2 (product)

#

x^2-(sum of root)x + (product of root) = 0

#

x^2-2ax+2a^2

#

-2a=-6, a=3

#

2a^2=b

#

b=18

#

@drowsy gust thats whati did

marsh citrusBOT
#

@dense lynx Has your question been resolved?

marsh citrusBOT
#
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mighty swift
#

find g^-1(x)

marsh citrusBOT
mighty swift
#

i got ans f^-1(x)=x-5/8

#

am i correct

glossy flint
#

No

hard gull
#

f(f^-1(x)) = f^-1(f(x)) = x , u can verify urself using this

glossy flint
#

It's $\frac{x+5}{8}$

#

Ups

mighty swift
#

why +..

elfin berryBOT
#

Alberto Z.

glossy flint
mighty swift
#

i didnt get it.

#

can u write it like that pic thing

hard gull
#

show ur working

mighty swift
#

ok

#

one sec lol i was drinking water

#

Here

hard gull
#

when u send 5 to lhs. It becomes
y+5

mighty swift
#

we should replace y place with 8x , no?

hard gull
#

$$y = 8x - 5 $$
Adding 5 on both sides
$$y + 5 = 8x - 5 + 5$$
$$ y + 5 = 8x \cancel{-5} \cancel{+5}$$

elfin berryBOT
#

JustToPro

hard gull
#

$$y + 5 = 8x$$

elfin berryBOT
#

JustToPro

mighty swift
#

oh

#

ok thanks i get it noww

marsh citrusBOT
#

@mighty swift Has your question been resolved?

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mighty swift
#

.reopen

marsh citrusBOT
#

โœ…

mighty swift
#

i got ans 2/-5

glossy flint
#

No, pay attention to the sign

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When you square something you can't get a negative thing

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xยฒ = xโ€ขx
If x < 0, you get negโ€ขneg = pos
If x > 0, you get posโ€ขpos = pos

In both cases the result is positive

mighty swift
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..

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shouldnt we replace x^2

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by -5

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??????

glossy flint
#

Why??

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f(-5) means replacing x with -5

mighty swift
#

but x^2 is still x

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tho

glossy flint
#

xยฒ is xยฒ, x is x

mighty swift
#

exponent stays same?

glossy flint
glossy flint
mighty swift
#

like (-5)^2

glossy flint
#

Yes, that's xยฒ when x=-5

mighty swift
#

oh

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so final

#

ans

#

is

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2/25

glossy flint
mighty swift
#

ohh

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okkk thanks

marsh citrusBOT
#

@mighty swift Has your question been resolved?

marsh citrusBOT
#
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rocky scaffold
#

Stuck after this

marsh citrusBOT
rocky scaffold
#

Used kings rule

crystal wraith
#

whats that ive circled

rocky scaffold
#

Split 0 to pi/2 into 2 parts basically

crystal wraith
#

No.

rocky scaffold
#

Same thing written with different limit

crystal wraith
#

Is it sin(pi/4-x)

rocky scaffold
#

Yes

crystal wraith
#

It's incorrect.

#

It should be a+b-x

rocky scaffold
#

Sin (pi/4 -x) + (cos pi/4-x)

crystal wraith
#

pi/2+pi/4 - x

rocky scaffold
#

Oh right

#

Youre right

#

Thanks

#

That was a horrible mistkae

#

.close

marsh citrusBOT
#
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Remember:
โ€ข Ask your math question in a clear, concise manner.
โ€ข Show your work, and if possible, explain where you are stuck.
โ€ข After 15 minutes, feel free to ping <@&286206848099549185>.
โ€ข Type the command .close to free the channel when you're done.
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ebon depot
#

The matrix $A_{3x3}$ has the determinant, $det(A) = 2$ \
Calculate: $det(3A^2)$

elfin berryBOT
#

Merineth

ebon depot
#

Do i form an equation or how do i go about solving this?

spark crystal
spark crystal
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for n is matrix n x n

ebon depot
#

Hmm

spark crystal
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wait a sec

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lemme recheck

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ye its ok

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try solve it @ebon depot

ebon depot
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I'm not sure what i'm trying to solve

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$det(kA) = k^n det(A) \
det(A^m) = (det A)^m$

elfin berryBOT
#

Merineth

ebon depot
#

this?

spark crystal
#

that 2 equation is Properties of Determinants

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using that 2 equation to solve ur problem

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det(3A^2) = k^n (det(A^2))

ebon depot
#

Determinants has so many properties i sadly don't know them by heart

spark crystal
ebon depot
#

These are the properties we are given

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I assume the two you gave are the first two

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Or nvm

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They don't seem to be the properties you gave

spark crystal
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it prove this one

ebon depot
#

Oh okay

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So how do i go about using these two equations

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what is m and n also

spark crystal
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let me give u and example

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it might easier

ebon depot
#

Ok!

spark crystal
#

for this is just say for the properties of power
Ex. det(A^2) = (detA)^2

ebon depot
#

Ah oki

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Can't we say that

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$det(3A^2) = (det(3A))^2$

elfin berryBOT
#

Merineth

spark crystal
#

yes

ebon depot
#

any way we can apply a property to remove the 3 from inside the det?

spark crystal
#

for this

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Its Matrix 3x3 so n =3

ebon depot
#

ohh

spark crystal
#

det(3A) = 3^3 det(A)

ebon depot
#

$(3^3det(A))^2$

elfin berryBOT
#

Merineth

spark crystal
#

$3^3(det(A))^2$

elfin berryBOT
#

Flwo : 004

spark crystal
#

this one

ebon depot
#

why does 3^3 move outside the ()?

spark crystal
#

wait me a sec lemme get my book

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for me ill say idk

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my master just me teach me like that

ebon depot
#

haha well it's ok i'll look it up in my own time

#

tysm for the help

#

๐Ÿซถ

#

.close

marsh citrusBOT
#
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ebon depot
#

.reopen

marsh citrusBOT
#

โœ…

ebon depot
frail orbit
#

oh boy

ebon depot
#

@spark crystalSince you know determinants.
Do i need to find A^-1 here if i want to determine det(A^{-1})

spark crystal
#

if it help some way

novel juniper
ebon depot
#

Yeah i was just about to mention that

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I rewrote it as 1 / detA

novel juniper
#

oh, find $A^{-1}$

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?

elfin berryBOT
#

Why am. I here

frail orbit
#

wait is it

ebon depot
#

yeah so sorry will fix it

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There we go

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It says "Calculate det(A^-1)"

frail orbit
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AHHH

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thank god

spark crystal
#

so find det(A) then do 1/det(A)

ebon depot
#

Funny enough he writes "Do you need to find A^-1?"

spark crystal
#

i hate to inverse matrix

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its too long

novel juniper
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IMO applying some row transformations to get as many 0s as possible may be a good idea

ebon depot
#

I've never done det on anything greater than 3x3 matrix.
Does the method for 3x3 apply for 4x4?

novel juniper
#

which, the det formula or transformations?

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afaik, the formula applies for a nby n matrix

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I could be wrong though

ebon depot
#

I was thinking something like this

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WIll take an eternity to calculate lmao

ebon depot
#

Because trying to apply the method as he does in the video

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will leave me prone for error

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with so much calculations

novel juniper
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yeah, but I don't see any obvious transformations

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oh

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nvm,

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I do now

ebon depot
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Am i allowed to manipulate it as much as i want?

novel juniper
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I think so

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there is one transformation that will give you 2 0s striaght away

ebon depot
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Hmm let me see if i also see it

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first row times -1 and adding that to row 4?

novel juniper
#

hint:- ||look at the top right ||

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the 4 elements there to be precise

ebon depot
#

the 4th column are all multiples of each other?

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I'm very bad at identifying stuff like that

novel juniper
#

the 4 elements on the top right are identical

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I;ll show what I mean

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just a mo

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\begin{pmatrix}
1 & 2 \
1 & 2
\end{pmatrix}

elfin berryBOT
#

Why am. I here
Compile Error! Click the errors reaction for more information.
(You may edit your message to recompile.)

novel juniper
#

these elements

ebon depot
#

so if i take the first row * -1 and add it to the second row

frail orbit
novel juniper
ebon depot
#

oh right

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So it'd become something like this?

novel juniper
#

uh, you want 0s in the first Row IMO

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so do it the other way round, atelast I always expand a det wrt the first row, so that's what I'm comfortable with

ebon depot
#

Hmm

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Afaik we wont get any 4x4 matrixes on the exam

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so i probably will just use a online det calculator

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This is a lot of calculation which i don't know lol

spark crystal
ebon depot
#

I want to but i've been at it since 10 am

spark crystal
#

i mean

ebon depot
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mentally exhausted so i'm not sure i'll be even able to

spark crystal
#

it in my test at high school

ebon depot
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Ok :)

spark crystal
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but it quardratic form

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like x+y+z = 15
and 2 more equation

ebon depot
#

So now i apply the method?

novel juniper
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yes

ebon depot
#

Now i only get 2 3x3 matrices ?

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since two of the constants are zero

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?

novel juniper
#

yeah

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the sum of 2 3by3 dets

ebon depot
#

i got it to be 55

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which is wrong

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i knew i'd do it wrong

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Any idea where?

novel juniper
#

what's the answer?

ebon depot
#

I got mine to be 55