#help-13

1 messages · Page 167 of 1

royal loom
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quick example

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what is the column space of $\begin{bmatrix} 1 & 0 \ 0 & 1 \end{bmatrix}$

wraith daggerBOT
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Austan

noble perch
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(x,y)

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cuz you can add em to get like a two dimensional plane

royal loom
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I wouldn't write it like that, but I see what you mean. Say R2 instead

noble perch
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oh

royal loom
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all 2D vectors

noble perch
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right

royal loom
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(real 2D vectors)

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Okay but what if I added another vector

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what if it was

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$\begin{bmatrix} 1 & 0 & 1\ 0 & 1 & 1 \end{bmatrix}$

wraith daggerBOT
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Austan

royal loom
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what's the column space of that?

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can we get anywhere new? is there any more linear combinations we can reach that we couldn't before?

noble perch
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well the vector in column 3 is linearly dependent on the first two columns

royal loom
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yup perfect

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so no

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we can't

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the column space is unchanged if we ignore dependent columns

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so when we row reduce a matrix and find its pivot columns

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we find out what columns are dependent

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we ignore these

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and make our column space from the pivot columns

noble perch
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oh okay

royal loom
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$$A=\begin{bmatrix} 1 & 0 \ 0 & 1 \end{bmatrix}$$
$$B=\begin{bmatrix} 1 & 0 & 1 \ 0 & 1 & 1 \end{bmatrix}$$
$$C(A)=c_1 \cdot \begin{bmatrix} 1 \ 0 \end{bmatrix} + c_2 \cdot \begin{bmatrix} 0 \ 1 \end{bmatrix} = C(B)=\mathbb{R}^{2}$$
Because the pivot columns of $A$ and $B$ are the same.

wraith daggerBOT
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Austan

royal loom
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C(A) meaning column space of A

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C(B) meaning column space of B

noble perch
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yeah this makes a lot of sense

royal loom
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now if you understand column space, row space should come easy. It is the same idea but for the rows

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if we want to know the row space of our matrix

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all we have to do is make the rows columns

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and find the column space of that

noble perch
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transpose

royal loom
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yes

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exactly

noble perch
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right

royal loom
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So are you feeling good about all of this?

noble perch
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so what would we do if the question asked us for the basis of the column space

royal loom
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do you know what a 'basis' is?

noble perch
noble perch
royal loom
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a basis of a space, is a set of linearly independent vectors, that span a space

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yes

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so for R2

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a basis can be

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<1,0>, <0,1>

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right?

noble perch
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yeah

royal loom
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those are linearly independent

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they span R2

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so they form a basis for R2

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how about

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<5,1>, <0,8>

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do those form a basis for R2?

noble perch
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id say they do

royal loom
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yes

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actually there can be infinitely different choices of basis's for any given space. Usually we like to choose the simplest one possible

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for R2 we would normally choose <1,0>, <0,1>

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right

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okay

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so earlier we said that

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the column space, is the space spanned by the linear combinations of your columns

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if we want a basis for the column space

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we want to find linear independent vectors, in our column space, whose linear combinations fill the space

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you should have a good idea of where to find these

noble perch
royal loom
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yes they will 99% likely only ask you for one basis

noble perch
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let me do a problem on bases and i'll be back

royal loom
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okay, I have to go for now, but my final hint to you is that there was a reason we found the pivot columns

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you can DM me if you need more help but I wont get to it until later

royal loom
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not in REF no

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but the columns in the original matrix, that are pivot columns in REF

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yes

noble perch
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ah okay

noble perch
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.close

cedar kilnBOT
#
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crimson sedge
cedar kilnBOT
umbral dew
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!status

cedar kilnBOT
#
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6. None of the above
crimson sedge
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1

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1

dire geode
crimson sedge
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FTC

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?

dire geode
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,tex .FTC1

wraith daggerBOT
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riemann

dire geode
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F' = f

crimson sedge
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Oh

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Ok

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How do you know that but are you an iitian

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Ok thanks @dire geode

#

.close

cedar kilnBOT
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grizzled scarab
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hey, im trying to prove that +mod3 is associative and having some trouble

grizzled scarab
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binary operation on the group {0,1,2}

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I end up with versions of this and I can't really get it to be the same on both sides but my book says otherwise, also checking it seems like it is associative
Any help?

crimson delta
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you cant just divide by 3 like that

nimble mulch
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  • or *?
grizzled scarab
grizzled scarab
nimble mulch
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ok you'd rather do ([a]+[b])+[c] ≡ ([a+b])+[c] ≡ [a+b]+[c] ≡ [a+b+c] ≡ [a]+[b+c] ≡ [a]+([b+c]) ≡ [a]+([b]+[c])

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you usually never specifically apply mod n or division by n in the modulo set for n

grizzled scarab
nimble mulch
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I presume you're familiar with the notation [x] in a Residue Class Ring

grizzled scarab
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I am not 😅

nimble mulch
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e.g. in the Ring Z/5Z: [0] ≡ [5] ≡ [10] ≡ [15] ≡ ...

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let me adjust that for the above proof as well

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@grizzled scarab if you just take this general notation the proofs of the properties of the Ring become simpler

grizzled scarab
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Idk what you mean by ring, I'd try to read English is not my native as well

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But I probably can't use that in my course since I didn't learn it

nimble mulch
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what's your native, possible they match

grizzled scarab
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I speak Hebrew

nimble mulch
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kk nvm

grizzled scarab
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Is there another way to prove this? Kinda in the way I did it that makes sense at all?

nimble mulch
nimble mulch
grizzled scarab
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Yes

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I forgot to define

nimble mulch
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I mean if you work with modulo operations you'd usually also at least have to be able to use equivalence classes

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which are denoted by [x]

nimble mulch
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you need to be able to somehow intertwine addition and the modulo operation, which you'd do via equivalence classes

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@grizzled scarab like could you provide what operations and properties you've already learnt / area allowed to use

grizzled scarab
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Pretty much nothing, it's like first course of uni and this is the beginning but this course assume no previous background

nimble mulch
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the approach of rewriting a modulo addition as an addition and integer division seems rather sloppy

grizzled scarab
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I'll have to look into the stuff you said and ask my teacher

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I appreciate the info

nimble mulch
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since within Z/3Z, the number 0 suddenly is equivalent to 3

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as well as to 6, 9, etc.

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so you need to define this behavior as equivalence

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and then you end up with equivalence classes @grizzled scarab

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{0,3,6,9,12,15,...}

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{1,4,7,10,13,...}

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{2,5,8,11,14,...}

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all numbers within these sets are equivalent to each other within Z/3Z

grizzled scarab
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Yea they didn't really do that I guess, just said you divide and take remaineder = modulo

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If I understand what you mean

nimble mulch
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with your half addition symbol

grizzled scarab
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I think I have to ask my teacher for clarification

nimble mulch
grizzled scarab
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But you gave me a direction now

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Yes

nimble mulch
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k, because then the only missing step is

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that you want to summarize these equivalence classes with a notation

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because 0 would have the same meaning as 3 etc.

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which is where the notation [n] comes in

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so [0] stands for the equivalence class of 0

grizzled scarab
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Ah I think I understand you now

nimble mulch
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when you write [0]+[1]

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you don't "add" sets together, but you add equivalence classes

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[0]+[1] = [1]

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[2]+[2]=[4]=[1]

grizzled scarab
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I'll read about it some more and look for more examples too regardless

grizzled scarab
nimble mulch
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kk, I'll again refer to the initial proof I provided, because that's how you'd prove it almost always

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most definitely not with translating division and taking the remainder using symbols

grizzled scarab
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Thanks again for all the info!

nimble mulch
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[2]+[2] = [2+2] = [4] = [1] (within Z/3Z)

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so yeah, I'd just write down this proof, you'll quickly grasp it

cedar kilnBOT
#

@grizzled scarab Has your question been resolved?

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cedar kilnBOT
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#

Please don't occupy multiple help channels.

royal loom
#

@coarse shadow Stick to one channel

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post your question here

cedar kilnBOT
#
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jaunty mural
royal loom
coarse shadow
#

with this

royal loom
#

this channel is going to close soon because you deleted the original message

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you need to open a new channel for your questio

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!help

cedar kilnBOT
coarse shadow
#

how do I add images because I need to upload the math problem

dire geode
cedar kilnBOT
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bold totem
#

$\frac{dy}{dx}=\frac{sin^3x}{tan^2y}$

cedar kilnBOT
#

Please don't occupy multiple help channels.

wraith daggerBOT
bold totem
#

(differential equation)

stuck walrus
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It's separable

magic solar
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Multiply by tan ^2y to the LHS and move the dx to the RHS and integrate

cedar kilnBOT
#

@bold totem Has your question been resolved?

cedar kilnBOT
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teal kraken
#

what does « determine the roots unity » mean?

stuck walrus
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Determine values of x for which x^n = 1

teal kraken
#

ok

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so just

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roots of unity?

stuck walrus
teal kraken
#

ik that one just not sure what my teacher means 😭😭

stuck walrus
#

might have missed out an "of" probably a typo

teal kraken
#

that makes sense

#

thank you!

#

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cedar kilnBOT
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cedar kilnBOT
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young dome
#

With what

cedar kilnBOT
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cedar kilnBOT
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chrome atlas
#

Can I get help with Statcrunch statistics software?

flint plinth
#

(i don't know the software myself)

chrome atlas
#

ok thank you

#

.close

cedar kilnBOT
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cedar kilnBOT
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spare narwhal
#

I need help with this question

cedar kilnBOT
tropic oxide
#

!status

cedar kilnBOT
#
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'm told it's wrong
4. I got an answer and would like my work checked
5. I have a question about someone else's worked solution
6. None of the above
tropic oxide
#

@spare narwhal

spare narwhal
#

2

tropic oxide
#

show current progress

spare narwhal
tropic oxide
#

right ok

#

so far so good except for the way you write your fives and sevens.

spare narwhal
#

Wym

tropic oxide
#

your 7's should have a stroke through them, and your 5's should not be looking like S's

spare narwhal
#

How should I write a 5 then

tropic oxide
#

two strokes

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one moment, let me show you

spare narwhal
#

Ohh

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Lemme try it and you tell me if it looks better

tropic oxide
#

ok

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stroke your sevens also

spare narwhal
#

Okay

tropic oxide
#

once you fix all this:

solve for x from the equation 3x+c = 5x - 13/2, and solve for y from the equation 3y + c = 5y - 7.
both x and y will be expressed in terms of c.

spare narwhal
tropic oxide
#

the leftmost 5 and 7 look the best

spare narwhal
#

I've always written my 5's like the other way so this is a change

tropic oxide
#

and those fives are VERY misreadable as S. and vice versa.

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mistakes like that are very hard to track down later lol

spare narwhal
#

Ah

tropic oxide
#

ok yeah good now do it for y

spare narwhal
#

@tropic oxide

tropic oxide
#

??

spare narwhal
#

Okay

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Okay what next

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I got y=1/2c+7/2

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@tropic oxide

tropic oxide
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ok yeah that's correct

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now calculate x-y and choose the right answer option based on that

spare narwhal
#

I got a as my answer

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@tropic oxide

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.close

cedar kilnBOT
#
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tropic oxide
#

yeah checks out

cedar kilnBOT
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jolly sable
cedar kilnBOT
jolly sable
#

I want to understand this formula

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I guess it is dot product of two vectors

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a,b,c are normal vectors and x-x1,y-y1,z-z1 are plane vectors

crimson sedge
jolly sable
#

yes

crimson sedge
#

$$x-x_1$$ looks like $$\Delta x$$ to me

wraith daggerBOT
#

One person

jolly sable
#

yes

#

so

cedar kilnBOT
#

@jolly sable Has your question been resolved?

knotty salmon
#

Hey

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I am very poor in maths

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Can anyone help me

cedar kilnBOT
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jolly sable
#

.reopen

cedar kilnBOT
#

jolly sable
#

.close

cedar kilnBOT
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jolly sable
#

How to find the equation of a plane which passes through middle point (3,-2,1)(1,4,-3)

lunar lynx
cedar kilnBOT
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cursive path
#

Can someone explain integration of area under graph

cursive path
#

for negative area questions?

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Do I just add a negative sign in front of the whole equation?

crimson sedge
cursive path
#

Do I split this into 2 parts

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the negative area and positive area?

slate lintel
#

yeah

crimson sedge
cursive path
#

But that part is negative area sir

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I will have to put a negative sign in front of the equation

crimson sedge
#

mmmmm kinda confusing question

cursive path
#

Like if I integrate area within sin x

crimson sedge
#

it could be either one because the area under the x axis would be considered negative in most cases. It never asked you to consider it not negative either

cursive path
#

I cant set the lower and upper bound to be 0 and 2pi

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wont that give me an area of 0

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since the 2 symmetrical areas will cancel out

crimson sedge
cursive path
#

Shouldnt it be positive area

crimson sedge
#

not unless you were asked to consider the area under the theta axis to be non-negative

cursive path
#

Im confused now

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So we always say that areas under the x-axis is negative areas

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and minus them off the total area?

crimson sedge
#

idk about always

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but I learnt that if the area is under the x-axis it's negative

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it should be negative unless the question says otherwise

cursive path
#

Coz I had questions before

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that showed a graph purely under the x-axis

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and they asked to find the area bounded

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the answer gave a positive number

cedar kilnBOT
#

@cursive path Has your question been resolved?

cedar kilnBOT
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strange horizon
#

if i have integral(1/(-e^(-y))dy, whats the solution?

urban orchid
#

3cosy+coty=0 (solve for x)

stiff totem
wraith daggerBOT
#

Desync

stiff totem
#

then it should be a recognisable integral

cedar kilnBOT
#

@strange horizon Has your question been resolved?

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urban orchid
#

<@&286206848099549185>

cedar kilnBOT
#

Please don't occupy multiple help channels.

royal loom
#

.close

cedar kilnBOT
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crimson sedge
cedar kilnBOT
crimson sedge
#

$$ v_{pa} = v_{pb} + v_{ba}$$

wraith daggerBOT
#

One person

crimson sedge
#

$$ 50 = v_{pb} + 50$$

wraith daggerBOT
#

One person

crimson sedge
#

$$v_{pb} = 0$$

wraith daggerBOT
#

One person

crimson sedge
#

The particle p relatiive b has a velocity of zero

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so why does

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(b) say the distance between the two is increasing?

#

huh

#

idk?

#

its just numbers

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i assume that

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is b is staionary

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if a is staionary

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then b is moving 50 km away

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and p is moving 50 km away

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no

#

no picture

#

nope

#

oh wait

#

picture i never seen

cedar kilnBOT
#

@crimson sedge Has your question been resolved?

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thin tusk
#

A variant of Rod cutting problem, I know it's a Computer Science problem but it is also a Math problem and I want the mathematical approach for this question.
I have provided an image of the original question from the past ICPC problem, I have tried several things to find its best solution but I couldn't get to a valid solution, so I need someone who can help me understand this problem and find a solution.
the next three lines shows the result for each row
you can get to a maximum of 4 portions/pieces for the loaf of bread if the constant factor is 1.500000 (Float value in C++ which is up-to 6-to-7 decimal places)

cedar kilnBOT
#

@thin tusk Has your question been resolved?

thin tusk
#

I can try and find the largest possible cut by simple brute force and with a little trick

0.500000 / 1.5 = 1 / 3 = 0.333333 // upto 6-7 decimal places max
1.000000 - 0.333333 = 2 / 3 = 0.666667
0.6666667 > 0.4999995 // So this cut is not possible

// Now I aim for 0.666667
(2 / 3) / 1.5 = 4 / 9 = 0.444444
1 - 4 / 9 = 5 / 9 = 0.5555556
0.5555556 < 0.6666667 // Repeat this and you get to the largest possible cut.
// But it won't give me the optimal cut, but I can keep this approach going for a few more steps

// Now I aim for 0.5555556
(5 / 9) / 1.5 = 10 / 27 = 0.3703704
1 - (10 / 27) = 17 / 27 = 0.6296296
0.6296296 > 0.5555556 // This cut is not possible

// Now I aim for 0.6296296
(17 / 27) / 1.5 = 34 / 81 = 0.4197531
1 - 34 / 81 = 47 / 81 = 0.5802691
0.5802691 < 0.6296296 // Acceptable
// If I keep repeating it for n-steps I'll eventually get to the solution but it would take alot of operations which I don't want, it's not an optimal approach I want to find make sort of formula which would get me either the best first cut or the end state cut which in this case (k = 1.5) gives the result 0.214285.
// If a formula cannot be deviced then the next possible option is to find best cut with minimal operations.
cedar kilnBOT
#

@thin tusk Has your question been resolved?

thin tusk
#

Can i get some help?

#

<@&286206848099549185>

cedar kilnBOT
#

@thin tusk Has your question been resolved?

thin tusk
#

<@&286206848099549185>

cedar kilnBOT
#

@thin tusk Has your question been resolved?

thin tusk
#

<@&268886789983436800> waiting for a long time, still haven't gotten a single response

#

i need to close this ticket

worldly chasm
#

Many people on this server who can solve this were asleep when you asked, please be patient and only ping once.

#

Would a simple recursive process, where you cut the largest loaf such that you create a new smallest piece that is the (new largest piece)/k in size work? It's a greedy algorithm, so it might be suboptimal.

wanton sail
#

as it says in the instructions

#

please don't ping moderators about stuff like waiting for a long time

#

!volunteers

cedar kilnBOT
#

Helpers are just people volunteering their time to help you. Be polite.

thin tusk
#

the problem is the cutting part

worldly chasm
#

For instance, for k = 1.5

Loaf: 1.0
Let the size of the new loaf be n, Now we solve n = (1.0 - n)/k which gives n = 1.0/(k+1) or 0.4

Loaf: 0.6 0.4
We take the largest of these 0.6 and do the same trick, except we need to look at the 0.4 loaf or the 0.6 loaf depending on the size of the newest loaf, largest is better.

Looking at 0.4 we have n = 0.4/k = 0.2667

Looking at 0.6 we have n = (0.6 - n)/k => n = 0.6/(1+k) = 0.24

Because 0.2667 > 0.24 we take the former

Loaf: 0.3333 0.2667 0.4

Next, consider the two options for 0.4, which are 0.3333/1.5 = 0.2222 or 0.4/2.5 = 0.16, we find that 0.2222 is larger so we want to create that, however, doing so would create a loaf smaller than 0.2222 from the 0.4, so the best we can do is 0.2, which ends the iteration.

Loaf: 0.3333 0.2667 0.4

Given that a solution was provided that is better than this, a simple greedy algorithm seems like it cannot work.

thin tusk
#

need more accurate results than 0.6 and 0.4

#

how to reach those precise numbers

worldly chasm
#

I'm sorry?

#

Did you read what I wrote?

thin tusk
#

the first cut is 0.571429 and 0.428571

worldly chasm
#

Yes, I know. Please read all of the way through, it is not a solution, it is describing my attempt at a simple greedy solution that does not work

#

My guess is that the first cut is not unique, however

#

There are a range of values that will work.

#

And they are intentionally randomizing within this range to obscure the solution

#

Another attempt, let's find the smallest k such that you can make 3 loaves with any cuts.

If we make the first cut greedy to maximize the size difference between the two loaves, then we have

Loaf = 1/(k+1) k/(k+1)

Then we need a cut such that the larger loaf cut into half precisely is exactly equal to 1/(k(k+1)) which is k/(k+1) = 2/(k^2 + k), which implies k = sqrt(2)

#

So for k < sqrt(2) the best you can get is a single cut, for k >= sqrt(2) you can get at least 2 cuts (3 loaves).

#

And in the case where k exactly equals sqrt(2) this cut is unique. But for k = sqrt(2) + epsilon this cutting isn't unique, there is some "wiggle room".

#

I'll leave it to you to exactly determine how much wiggle room, it's just straightforward algebra. I'm going to move on to a minimal k for 3 cuts.

worldly chasm
#

So for three cuts we don't want to leave as large a second loaf as possible, but as large of a third(!) loaf as possible, which means our first cut should be less greedy.

If we have loaves of sizes a, b, c after two cuts, we want the largest loaf (a) to get cut exactly in half and be exactly b/k in size (where b is the second largest loaf).

c will come from the first cut, and a and b will be determined from the second cut.

First cut:

Loaf: a+b c

Subject to the constraint that a+b > c, a+b < ck.

Second cut: a b c

Subject to the constraint that ak = c, equality required for optimality.

Finally third cut: a b c/2 c/2

Subject to the constraint that ck/2 = b <= ak, equality is required for optimality here as well.

#

Using a computer algebra system, it looks as if, ironically, you can get a solution for 3 cuts with k = sqrt(2) as well???

#

It feels like I've made a mistake somewhere but I cannot see it.

#

@thin tusk I don't know whether or not this helps you see an approach, but it looks like kind of a mean problem to reason about.

#

at least mathematically

#

There is probably some recursive solution that, while it does a lot of work, should be fast enough to run in a single second because computers are good at this sort of thing?

cedar kilnBOT
#

@thin tusk Has your question been resolved?

thin tusk
worldly chasm
#

@thin tusk we're starting from the premise that we can only make 2 cuts, and trying to find the minimum k that will get us there.

worldly chasm
#

I did as well, unfortunately it is sub-optimal 😦

thin tusk
#

it didnt said I have to get that accurate result which was bothering me alot

#

i was thinking how they got to that result

#

those specific values which perfectly overlap with one another in smaller cuts

#

Loaf = 1/(k+1) plus k/(k+1)
How did you make this formula

worldly chasm
#

that's not really a formula, but a description of the size of the pieces in the loaf at this step

#

the first piece is 1/(k+1), the second piece is k/(k+1)

thin tusk
#

should there be a + sign in b/w?

worldly chasm
#

No, because it's not a formula

#

think of it as an array:

#

loaf = [1/(k+1), k/(k+1)]

thin tusk
#

ahh

thin tusk
worldly chasm
#

that's what that part is saying

#

but unfortunately, 0.4, being the absolute smallest cut you can make, is actually too small to work with the 3rd cut

thin tusk
#

the problem itself is solved with this simple approach but there's still a big mystery

#

how they got to that precise numbers

worldly chasm
#

I don't think that the problem is solved.

#

Because it's not optimal, and the problem specifies that you must cut the loaf into as many pieces as possible.

thin tusk
#

Any proof

#

atleast it gives a rough estimate

#

it might fail on some corner cases

worldly chasm
#

"indicating the maximal achievable"

#

and I think it probably fails in most cases.

#

because 1.5 doesn't seem like a special value

thin tusk
#

for 1.999, how many cuts can there be

#

lets assume the inputs are lower and upper bound

worldly chasm
#

a whole hell of a lot

thin tusk
#

1.000 and 1.999

worldly chasm
#

it's infinite for 2

thin tusk
#

they fixed it for 3 decimal places

#

not 1.9999999

worldly chasm
#

and for 1 <= k < sqrt(2) it's only 1.

thin tusk
#

so there might be a finite answer

worldly chasm
#

there is certainly a finite answer.

#

but my guess is that the value approaches infinite quite rapidly

thin tusk
#

only 6 decimal places after decimal

#

so ig below 1 million max cuts

worldly chasm
#

while your output is limited in precision, you could still in theory come up with a scenario where you output mostly 0.000000 and have more than 1 million entries, provided that you're keeping track of your numbers with enough internal precision

thin tusk
#

float will keep the result upto 6 decimal places for me so my answer wont search beyong 6-7 decimal places

worldly chasm
#

a single precision float only does 6-7 decimal digits of precision, yeah. This is probably why they're saying not to output more than that.

thin tusk
#

also I got close to the actual result with my first cut
0.5849625 and 0.4150375

worldly chasm
#

It looks, strangely enough, now that I've double checked, that sqrt(2) gets you both a second and a third cut.

#

k = sqrt(2) that is

thin tusk
#

i did log2(k)

worldly chasm
#

I do not immediately see why that would be a good idea.

#

Can you share your thoughts?

thin tusk
#

i was messing around with random inputs and i thought maybe log has something to do with this problem and i tried different bases of log

#

like log base k, log 10 and log 2

#

which gave a close enough result to actual

#

yea when I cant find a pattern, I do some trial and error

worldly chasm
#

so in other words, if you have a loaf = [a, b, c] with c the largest loaf, you try to make a cut such that [a, b, c (1 - log2(k)), c (log2(k))]? and if the smaller loaf is too small to satisfy the constraint you?

thin tusk
#

it has the same issue as your first approach

#

it might or most probably will fail at some point

#

since its not giving a precise cut as the test case

worldly chasm
#

3/7

thin tusk
#

O_O

worldly chasm
#

I do not know why 3/7

#

and the k=1.6 starts off with 25/61

thin tusk
#

how in the what

#

can you make a table for values from 1.0 to 1.9

#

we can see a pattern emerge from it

#

also how is the first cut 25/61 for 1.6

worldly chasm
#

k=1.5 cuts are 3/7, 2/7, 3/14
k=1.6 cuts are 25/61, 16/61, 25/122, 10/61, 8/61

#

I'm not solving this, I'm determining a simple rational fraction pattern given the decimal numbers.

#

these are all quite close, and all have related denominators, so I'm confident that there is some underlying pattern that they are exploiting.

thin tusk
#

why even 61, thats such an absurd number to pick

worldly chasm
#

I do not know

thin tusk
#

surely if we dig deeper we can find their hidden pattern

worldly chasm
#

If you have any other examples of valid output from the oracle function, it would be appreciated.

thin tusk
#

they only provided 2 test cases

worldly chasm
#

So:

k=1.5

Loaf: [1]
Loaf: [4/7, 3/7]
Loaf: [2/7, 2/7, 3/7]
Loaf: [2/7, 2/7, 3/14, 3/14]

was the strategy

#

which seems more reasonable.

#

you make the initial cut, then cut each other in half.

#

k=1.6

Loaf: [1]
Loaf: [36/61, 25/61] (interesting that they're using perfect squares here)
Loaf: [20/61, 16/61, 25/61]
Loaf: [20/61, 16/61, 25/122, 25/122]
Loaf: [10/61, 10/61, 16/61, 25/122, 25/122]
Loaf: [10/61, 10/61, 8/61, 8/61, 25/122, 25/122]

thin tusk
#

perfect squares and a random prime as denominator (random to us for now)

#

with this pattern the next number should be
k: 1.7
49/85, 36/85

worldly chasm
#

that doesn't seem to follow

thin tusk
#

adding consecutive perfect squares

worldly chasm
#

well, there's no reason to assume that it's going to be linear (and every reason to assume it's not, as k=2 is literally infinite), and moreover the k = 1.5 case didn't feature consecutive perfect squares

thin tusk
#

maybe the jump is a little bigger b/w squares

#

ik the ICPC test questions have a really well constructed pattern, they always do

worldly chasm
#

oh, this is a programming competition

#

not homework

thin tusk
#

an old paper

thin tusk
#

i dont want to look at the solution online, I would rather discuss it with someone else and approach the solution from scratch

thin tusk
worldly chasm
#

I noticed.

#

it looks like historically ICPC problems at least from where I found, are numbered as problem A, not problem 1.

thin tusk
#

trying to make them a perfect square

worldly chasm
#

Yes, but you'll be unable to make a perfect square, because you'd have to find a common factor such that you have 2^2 * 2^x 3^y = 2^2n 3^2m, and also 3 * 2^x 3^y = 2^2j 3^2k, this implies that 2n = 1 + x, but 2j = x, but both 1+x and x cannot be even.

thin tusk
#

I'll probably think of new patterns while counting sheeps in my sleep

worldly chasm
#

@thin tusk before you go, a potentially useful observation

#

16, 20, 25 have common differences of 4 and then 5

#

36 and 25 the difference is 11

#

The algorithm might have the following structure:

thin tusk
worldly chasm
#

4^2, 4*5, and 5^2 ?

#

Dunno

#

That might be a coincidence or it might not

thin tusk
#

does the same apply for k=1.5?

#

4/7, 3/7
2/7, 2/7, 3/7

worldly chasm
#

Well in that case the common difference in the numerator is just 1

#

I'm looking at the algorithm in two steps, first we try to divide the bins in a specific way, then cut them all in half

#

Then it terminates unable to do more

thin tusk
#

i have to take a deeper look into Strassen multiplication algo after this one is solved

#

F

#

@worldly chasm

#
1/(k+1) = 1/(1.6+1) = 1/2.6 = 5/13

take square of numerator and you get 25

worldly chasm
#

hmmmm....

thin tusk
#

1/(1.5+1) = 1/2.5 = 2/5
take square of 2 u get 4

#

for k=1.7
i got 10/27 one half must be 100

#

is there a Pythagoras Theorem hidden in this

worldly chasm
#

I don't think it's quite that simple.

#

So one thing you've missed is that in the 1.5 case, you're taking the square of 2 to get 4, but 4 is the larger of the two numbers.

thin tusk
#

in this case its 25 the lower bound

worldly chasm
#

whereas in the 1.6 case, you're taking the square of 5 to get 25, but 25 is the smaller of the two numbers.

thin tusk
#

yea i noticed

worldly chasm
#

so I think this is just a coincidence

#

law of small numbers thing

thin tusk
#

well gn for now, i'll continue this struggle later today

worldly chasm
#

good luck

cedar kilnBOT
#

@thin tusk Has your question been resolved?

thin tusk
#

.close

cedar kilnBOT
#
Channel closed

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#
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tough fulcrum
cedar kilnBOT
tough fulcrum
#

my answer for (b) is wrong and I'mm not sure why

#

pls help

cedar kilnBOT
#

@tough fulcrum Has your question been resolved?

wanton sail
#

Hey! lemme take a look

wanton sail
# tough fulcrum

you found the correct value of lambda (20/33) but you just made a typo when calculating y

#

so your answer is basically right, just a small arithmetic mistake at the end :)

tough fulcrum
#

thanks for your help

#

.close

cedar kilnBOT
#
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wanton sail
#

no problem!

cedar kilnBOT
#
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supple mantle
#

how am I not sophisticated enough to see why this x just vanishes bruh: I wanna set 2x ln(x) +x = 0 to find critical points | Actually just got a grasp on it while writing this question, is it because we can just find the 0 of the factor and that will do? Are there other ways to find the 0 too?

supple mantle
#

cuz then it's just $ln(x) = \frac{-1}{2}$ then $ e^{-0.5}$

wraith daggerBOT
glass sky
#

i mean x can be 0 and e^-0.5 if im not wrong

supple mantle
#

yea, it's just that 0 is not that useful when finding the absolute minimum

idle cedar
#

but x cant really be 0 can it ?

#

because ln(0) is not defined

supple mantle
#

and that yea, 0 is not in the domain

idle cedar
#

therefore , as a product equals 0 iff one of the factors is 0 , x=0 is not an option

#

meaning the first factor has to be 0 , therefore you can drop x

supple mantle
#

yup!

#

thanks

#

.close

cedar kilnBOT
#
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unique isle
#

how do i solve this one?

cedar kilnBOT
unique isle
#

is there a formula or something?

proud arrow
#

allowed to use calculator?

unique isle
#

yeah

proud arrow
#

do you see the two R's

#

which make the arc

#

dont you see a triangle

#

that too isoceles

unique isle
#

yea

#

what are the r s though

proud arrow
#

could you apply some trigono metric properties over here?

proud arrow
#

if you see closely

unique isle
#

ok

proud arrow
#

try going over basic definitions of

#

them functions

#

oh yes how about we drop a line from ground to the plane

#

straight line

#

that'll make it easier to apply trig

unique isle
#

ook

proud arrow
#

could you see how we are gonna apply trig

cedar kilnBOT
#

@unique isle Has your question been resolved?

unique isle
#

no

#

i dont understand

#

i lost the plot

crimson sedge
#

You get r from this

#

Then use trigonometry by dropping an altitude from centre of plane to vertex

#

sin(0.5) ≈ 0.5

#

No wait that's radian

#

You're given degrees

#

sin(0.5°) = 0.008

#

And sin(0.25°) = 0.004

#

Use these to get answer

#

@unique isle

unique isle
#

okok

#

let me try

cedar kilnBOT
#
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cedar kilnBOT
#
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crimson sedge
#

How would I go about solving this without doing any actual "calculations"

crimson sedge
#

the if part seems weird

cedar kilnBOT
#

@crimson sedge Has your question been resolved?

crimson sedge
#

<@&286206848099549185> you don't have to read the question at all

#

Just asking

#

how I would get rid of the if statement

worldly chasm
#

You cannot 😦

#

At least not without using functions that are essentially if statements

#

Like the indicator function or floor function or similar

crimson sedge
#

oh yeah

#

I could

#

hmm

#

use that

#

do like

#

$$sign(\Delta x - d_1)$$

wraith daggerBOT
#

One person

crimson sedge
#

but still

worldly chasm
#

Let u(x) be the function that gives 0 if x is negative and 1 of u(x) is positive (undefined at 0), u(x - Δx) will return 1 if plateau and 0 if ramp

#

And undefined if it lands on the corner

#

But I'm not sure what you're planning on using this information for?

crimson sedge
#

just learning

#

how not to

#

do math when doing math

worldly chasm
#

Are you trying to come up with a general formula for b) and c) without using cases?

crimson sedge
#

yes

worldly chasm
#

Probably not worth it imo. Cases are cleaner and clearer.

#

The purpose of writing down math as math is to communicate the result with yourself and anyone else who reads it

#

The less that person needs to think to understand it, the better, imo

#

There's obviously a lower bound of thinking effort, but the expression itself shouldn't hinder understanding but facilitate it as much as possible.

crimson sedge
#

wait nvm

#

literally exact same situation

#

I was gonna ask

#

How to answer True/False statement with math

#

I did this for a

#

Got kinda lazy

#

and didn't make variables for some things

crimson sedge
#

.close

cedar kilnBOT
#
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#
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shadow kite
#

Can someone help me with this, I’m not sure how to proceed

shadow kite
celest ledge
#

It’s sqrt(log(-x))=log (|x|)

#

Now x<0 so sqrt(log(-x))=log(-x)

#

log(-x)=0 or 1

#

sqrt(x^2) is |x| not x

cedar kilnBOT
#

@shadow kite Has your question been resolved?

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cedar kilnBOT
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primal lodge
#

How am i supposed to do this?

#

I guess i could plot the rectangle

#

Do i just reflect every point?

upbeat forge
primal lodge
#

i guess it was just cuz i sketched wrong

#

looks like a straight forward question

#

should probs try again

#

okay yeah i got it

#

bad diagram lol

#

.close

cedar kilnBOT
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crimson sedge
#

How???

cedar kilnBOT
glossy mango
#

it says log 2 = m

#

and than asks us to find log 25 in terms of x

#

does it mean in terms of m?

tropic oxide
#

yes most likely it's just a typo

crimson sedge
#

Yes it means in terms on m

#

But I still can’t do it

#

That’s why I asked this question, just to clarify

#

@glossy mango

glossy mango
#

log 10 is 1, obviously

#

smilarly, log 100 is 2

crimson sedge
#

yea...

glossy mango
#

log 100 - 2 log 2 is the same as log 100 - log 4 = log 25

#

and log 2 is m

crimson sedge
#

oooooooooo

glossy mango
#

so log 25 is 2(1-m)

crimson sedge
#

i get it now!

#

thank you!

glossy mango
#

np <3

crimson sedge
#

.clos

#

c.lose

#

.close

cedar kilnBOT
#
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crimson estuary
#

Just wondering if someone could see if its correct since i dont have the answers

ocean mural
#

if a = 2
and b = a - 14
b cannot be 4

crimson estuary
#

ah shit

#

can u help me find where i went wrong

ocean mural
#

well its probably right there

#

if a = 2

#

and b = a - 14

#

what is b. really

cinder venture
#

Is this an exam?

crimson estuary
#

its a past paper

crimson estuary
ocean mural
#

oh ok

crimson estuary
#

so i definitely got something wrong somewhere

ocean mural
crimson estuary
#

oh wait

#

so b does = -12

#

ok well thank you for helping

#

.close

cedar kilnBOT
#
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spring coyote
cedar kilnBOT
spring coyote
#

Guys

#

is this very small number?

#

below 0.05?

#

or very big

crimson sedge
#

What exactly?

#

7 is bigger than 0.5

#

So

spring coyote
#

h mmmm

ocean mural
#

70/100 = 0.7
70/1000 = 0.07
70/10000 = 0.007

spring coyote
#

oho

ocean mural
#

so 70/9999999 must be very small

spring coyote
#

like basically

cinder venture
spring coyote
#

i learn statistaks, and it say fraction of choice if its below 0.05 then use certain formula

ocean mural
#

I mean calculatro lol

spring coyote
#

and fraction of choice is base sample divided by total possible sample size

crimson sedge
#

Anyways e-6 Is basically 10^(-6)

spring coyote
#

ye

#

so i dont get why total number of surveyees in a theatre is theoretically infinite

#

its task where i dont know sample size

#

so i first need to deterimne n/N = fraction of choice translated

#

and textbook say

#

we can determine without calculating that its below 0.05 (which means we use special formula for below 0.05

#

because it is possible to survey infinite amout of people about what they think about theatre price

#

but humans are 8 billion

#

shiiiiiiiiiiii

#

so i calculate sample size is 70

cedar kilnBOT
#

@spring coyote Has your question been resolved?

cedar kilnBOT
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primal lodge
#

how would i do this?

cedar kilnBOT
primal lodge
#

not really sure where to start

stiff totem
#

you can fill in some of the missing angles, as they are opposite angles

#

as in, the angle where l and m meet is x degrees on both sides

#

so you can fill in one of the blanks at the bottom there

#

then, once you have all of them, do the replacements as given in the question (y=2w, v=110, etc.)

#

then they should add up to 360, which should give you something to work with

primal lodge
#

not sure why i didn't even think of even doing anything lol

stiff totem
#

yeah

primal lodge
stiff totem
#

yes

primal lodge
#

answer should be 3/4 ig

#

i have another question

#

I'm just reviewing questions from a practice test

#

but the way i approached this iirc was

#

y is either in (-15, 15)

#

and the other one involves the (-20,10)

#

i guess i could combine it, but i don't have to right?

#

The answer is D? I don't really have an answer key so just ocnfirming

stiff totem
#

x=8, y=-16 satisfies those inequalities, but so does x=8, y=-14

#

so yeah, can be either way, so d

primal lodge
#

thanks

#

.close

cedar kilnBOT
#
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cedar kilnBOT
#
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velvet lynx
#

Find Min

cedar kilnBOT
sly sandal
#

Min?

velvet lynx
slate lintel
#

are there constraints on x and y?

velvet lynx
south tundra
#

I thought there should be too, but realised it might just be about completing the squares

#

Try doing that

slate lintel
#

you've got an xy term so that will be fun for you

south tundra
#

Hint: ||Complete the square in x and y first and then in y||

#

Huh wait

#

That -2x hmmCat

vague rapids
#

Does a minimum even exist?

south tundra
#

Alright I found it

#

Yes it is possible

agile wyvern
#

just take the partial right?

south tundra
#

Actually

velvet lynx
south tundra
#

No nvm

agile wyvern
#

i got an answer

south tundra
vague rapids
#

you sure you are not missing any part of the question?

agile wyvern
#

oh

#

if you can use calc its simple

south tundra
#

Yeah can you show us the context?

velvet lynx
agile wyvern
#

oh

velvet lynx
#

NOoooooooooooooooooo

south tundra
#

Or does it just say "Find the minimum" and that's it

velvet lynx
#

the test said

#

cant use

#

calc

south tundra
#

By calc we mean calculus just in case

velvet lynx
vague rapids
#

Still, it would be better if you send an image

velvet lynx
#

Tìm giá trị nhỏ nhất của biểu thức:M=...

#

use translate

#

Giá trị nhỏ nhất đó đạt được khi x,y bằng bao nhiêu?

vague rapids
#

So there was a condition

#

x=y

junior dome
#

Find the minimum value of the expression: M=x(x + y) ) +y(y - 3) – 2x + 2010 What is the minimum value that is reached when x, y equals ?

vague rapids
#

wait did I misinterpret

junior dome
#

yeah i read it like that too

#

but there's ? sign

boreal ravine
#

math

velvet lynx
#

when M reach min what is x,y

junior dome
#

i think it is x = y tbh

#

? is for what is the min. value

#

and not for x and y

vague rapids
# velvet lynx no

Well, if the condition x=y is not given then there would be no minimum

vague rapids
#

,w minimum of x(x+y)+y(y-3)-2x+2010

junior dome
#

ahh

agile wyvern
#

thats what i got when i used calc but how do you do it without calc

cedar kilnBOT
#
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crimson sedge
#

making a circular candy braclet, you have four letters to choose from: a,b,c, (with only three candies for each letter), if you can create braclets of length 1-4, how many possible bracelets can you make?

crimson sedge
#

I said:
4 length = 3 * 3 * 3 * 2
3 length = 3 * 3 * 3
2 length = 3 * 3
1 lenght = 3

answer = 3 + 9 + 27 + 54 = 93
is this correct?
oh shoot i think thats wrong
because abc = bca =cab since its ciruclar

#

my next attempt:

#

length 1: 3

#

length 2: aa,ab,ac,bb,bc,cc = 6

#

im not sure how to do this recursively tho

fair geyser
#

it's not just circular it also has 2 sides

#

bca = bac

crimson sedge
#

nono

#

bca != bac

#

I dont think

fair geyser
#

in real life it is

#

depends if the intent of rthe question follows rl

crimson sedge
#

yea it does

#

it says specifically the LOOP of the chain

fair geyser
#

idk what you mean

crimson sedge
ocean mural
#

lol if it's circular then yes bca = bac

crimson sedge
#

such that abc = cab = bca

#

but abc != acb (=bac)

fair geyser
#

a real life bca bracelet is indistiguishable from bac

crimson sedge
#

oh

#

yea

#

i agree

#

so how many bracelets can she make

#

using up to 4 beads

#

that are UNIQUE

sharp mantle
#

Are we assuming the bracelet can be flipped

#

Or no

crimson sedge
#

no

#

doesnt state it so id assume not

sharp mantle
#

Then abc ≠ acb

ocean mural
#

well in real life bracelets can be flipped

crimson sedge
#

the only consideration is that you can loop one bead around

#

and abc -> cab

sharp mantle
#

So then they can't be flipped

crimson sedge
#

no

#

how would i approach this problemm

fair geyser
#

i don't know

crimson sedge
#

just writing them down?

cedar kilnBOT
#

@crimson sedge Has your question been resolved?

crimson sedge
#

<@&286206848099549185>

twin marsh
#

(Namely issues like abc = bca = cab).

cinder venture
#

Dont use ChatGPT for Math

#

May not always be correct

dire geode
#

<@&268886789983436800>

wanton sail
#

Please don't use ChatGPT, especially to answer questions from helpees @crimson sedge

crimson sedge
#

@dire geode you know how to do it?

crimson sedge
wanton sail
cedar kilnBOT
#

@crimson sedge Has your question been resolved?

cedar kilnBOT
#

@crimson sedge Has your question been resolved?

cedar kilnBOT
#
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After 15 minutes, feel free to ping <@&286206848099549185>.
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• Be polite and have a nice day!

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oblique prawn
#

yo

cedar kilnBOT
oblique prawn
#

is $\lim_{x\to 0^+}{\frac{1}{x}}$ equal to infinity or DNE

wraith daggerBOT
royal loom
#

depends

#

what is your definition for a right sided limit converging to infinity?

compact junco
#

technically it doesnt exist

#

but you can say its infiniy

oblique prawn
royal loom
#

yes

#

there can be

oblique prawn
#

so what would it be

#

Find $a$ and $b$ such that $\lim_{x\to 0}{\frac{\sqrt{ax+b}-3}{x}}=\frac{1}{3}$

wraith daggerBOT
royal loom
#

well

#

for a normal right handed limit

#

it is something like

#

we say $f(x)\to L$ as $x\to c^{+}$ if $\forall \varepsilon >0:\exists \delta >0$ s.t $\forall x \in S$ with $c<x<c+\delta \implies |f(x)-L|<\varepsilon$

wraith daggerBOT
#

Austin

royal loom
#

and then combine this with a definition for a limit going to infinity

#

and ya

oblique prawn
#

oh ok

#

ty

#

.close

cedar kilnBOT
#
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cedar kilnBOT
wraith daggerBOT
crimson sedge
#

Open the brackets

#

(x-5)-x = -5

#

In numerator

#

That's your last step stare

stark quest
#

x-5-x=-5

crimson sedge
#

Yeah

#

-5

#

Not just 5

#

No worries

cedar kilnBOT
#
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candid lotus
#

determine the exact value of:

cedar kilnBOT
candid lotus
#

what should i do here?

#

i need to apply formulas?

gritty viper
#

all of these have values you should know

#

like, every individual sin() and cos()

#

so you can just find those all

candid lotus
gritty viper
#

yeah

candid lotus
#

thats bcs i saw taht

#

i was confused

#

what is that for

gritty viper
#

well you could try using that but there's no need

#

those formulas are so cursed

#

it should be an exercise for very strong students to derive them from the normal ones (sin(a+b), etc) and then completely forget about them after

candid lotus
#

In bold and in blue, the new features at the start of sup

#

thats what im going to see this year

#

it has nothing to do with the revision exercises of last years im doing

gritty viper
#

ah ok

candid lotus
#

what studies are you doing or did you do btw? @gritty viper

gritty viper
#

nothing super focused yet

#

studying some mathematical logic on my own

candid lotus
gritty viper
#

idk

#

PhD

#

probably

candid lotus
#

alright i see, thats really nice

cedar kilnBOT
#

@candid lotus Has your question been resolved?

#
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cedar kilnBOT
flint plinth
#

como

dire geode
crimson sedge
#

yo como gatos

#

i ate a cat

sharp ginkgo
#

yo comí los gatos

#

bc that’s the past tense for it