#help-23

1 messages · Page 303 of 1

dense sage
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oh oka

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cool

left gyro
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I thought your syllabus directly taught you that equation

dense sage
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um

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not to my knowledge

left gyro
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in that case theres still something easier we can do

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originally we have the tangent line (y - h(k)) = h'(k) (x - k)

dense sage
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but i feel like the equation ur giving me is gonna be easier to use

left gyro
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the

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with h(k) at x = k, your point is at (k, h(k)) with slope h'(k)

dense sage
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yessir

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ohh that makes sense

left gyro
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now if you move the - h(k) to the other side, you get the y = h'(k) (x - k) + h(k) equation

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this is a common way to write the tangent line equation

dense sage
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oh and since h(k) is even then h(-k) is the same

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so c = c

left gyro
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not necessarily

dense sage
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oh wait wha

left gyro
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youre forgetting that its not in y = mx + b form

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its got an (x - k) there

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we'll need to address that

dense sage
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ohh ye

left gyro
flat frigateBOT
left gyro
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commonly the function is f, and the point's x-coordinate is either a or c

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if youre memorizing the equation, the convention is this one

dense sage
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oh oka

left gyro
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we're using the equation for our purposes, so our function is h and our coordinates are (k, h(k))

dense sage
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okaoka

left gyro
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now with y = h'(k) (x - k) + h(k),
you can expand (use distributive property on that h'(k) (x - k)

dense sage
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so h'(k) x - h'(k)k +h(k)

left gyro
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yep

dense sage
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okaa

left gyro
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now the slope is h'(k)

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and the y-intercept is h(k) - k h'(k) as shown by what you typed

dense sage
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okaa

left gyro
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now you can put in -k in and see what happens

dense sage
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okaa

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y = h'(k) x - h'(k)k +h(k)
y= m x + c

h(k) is even so h'(k) is odd and h'(-k) = -h'(k)

h(k) is even so h(-k) = h(k)

y= h'(-k) x - h'(-k) (-k) +h(-k)

y= - h'(k) x - h'(k) (-k) + h(k)

=- h'(k) x + h'(k) (k) + h(k)

so y = -mx + c

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is that right

left gyro
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unfortunately it isnt

dense sage
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oh no :c

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did i do smth weird

left gyro
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first youre beginning with y = mx + c instead of y = mx - c

dense sage
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oh oop

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there

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mb

left gyro
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next, it looks like you assumed h' is even

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h is even, so h' is odd

dense sage
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did i

left gyro
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around the - h'(-k) (-k) part, the next line says - h'(k) (-k)

dense sage
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neg neg

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right

left gyro
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yes

dense sage
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so y = h'(k) x - h'(k)k +h(k)
y= m x + c

h(k) is even so h'(k) is odd and h'(-k) = -h'(k)

h(k) is even so h(-k) = h(k)

y= h'(-k) x - h'(-k) (-k) +h(-k)

y= - h'(k) x + h'(k) (-k) + h(k)

=- h'(k) x - h'(k) (k) + h(k)

so y = -mx + c

left gyro
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yep

dense sage
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YAYYY

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THANK YOUUU

left gyro
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np

dense sage
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lifesaver!!!

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.close

safe radishBOT
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safe radishBOT
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whole acorn
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A test consists of 100 questions. A student gets 4, -1, or 0 marks, if he answers a question correctly, wrongly, or leave it blank, respectively. How many different total marks of the test are there?

safe radishBOT
#

@whole acorn Has your question been resolved?

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marble summit
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can someone help me with vector

safe radishBOT
marble summit
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If AB = u, and AF = v. Determine vector of DF

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here's my guest
DC = FA = -AF = -v
CO = BA = -AB = -u
DF = DC + 2CO = (-v) + 2(-u)

is that correct?

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i need someone actually know the answer, and i have some question

true horizon
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This is a regular hexagon?

marble summit
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yes

lime nexus
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im no mod but i dont think ur suppose to ping for helpers until 15mins later...

marble summit
marble summit
lime nexus
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it makes sense

lime nexus
wanton schooner
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u should end up with -2u-v whichever way u do

lime nexus
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theres many ways u could go about for it

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the way u did it is just i would say the fastest way?

marble summit
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yeah

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so it work with another side?

lime nexus
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mhmm

marble summit
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like DO or DE

lime nexus
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bc anyway u go, u will eventually reach -v -2u

lime nexus
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ur way is faster and more convenient

marble summit
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so it will be a triangle?

lime nexus
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sorry?

marble summit
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if im not right

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like this D to O and D to E

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and last one is O to F

lime nexus
marble summit
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ahh

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i see

lime nexus
marble summit
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so yeah, why is it reach to C?

lime nexus
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D to O to E to F will give DF

lime nexus
marble summit
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D to C is like why is it line up to C and not to
D to F instead and count it normally ( but still i dont get it with hexagon thing)

lime nexus
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in order to get from D to F, u can go from D to C to O to F, and it will give DF

lime nexus
marble summit
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bad thing discord mobile cant draw

lime nexus
marble summit
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yeah, wait i'll check on my computer 1 minute

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this is what am i trying to ask, why we dont do this

lime nexus
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if u do that, how are u able to find the vector for it?

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itll be too hard with what we are given with right?

marble summit
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ahh

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thats why

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so we can't?

lime nexus
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vectors is like if u wanna get from a certain point to anohter point, u can use vectors where u follow the given paths until u reach ur point

lime nexus
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wait

marble summit
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i mean, firstly when i try to find the vector was like that

lime nexus
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for the green parts, notice how CO is the same as AB but in the opposite direction, since we know AB = u, then CO is -u, and it happens twice, so thats why we minus u twice

marble summit
lime nexus
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and then we add the 3 vectors to get DF= -v - u -u

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hence DF = -v -2u

marble summit
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is there any other way?

lime nexus
lime nexus
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if u want to try doing it with the red way, i dont think it’s possible as we cant find what red vector is since there is no vector and values we can work with from the question

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ig qns like these, to solve it u would want to try find a path to get from where u want to go, by following other vectors and adding them up!

marble summit
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i see, so we just follow the instruction of the question? and try find a path

lime nexus
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mhmmm!

marble summit
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like find a similiar AF and AB and determine the vector ( consider the direction )

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okok i got this, thank you boss

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appreciate it

lime nexus
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so like AF and AO arent the same vector bc it goes into 2 diff directions that arent opposite directions and arent parallel at all

marble summit
lime nexus
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altho u can see that AF and CD are parallel and only thing different about the direction is its going opposite sides

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so thats why i deicded to make a path thru D to C to O to F, so i also dont need to deal with vectors going in the direction of AO

lime nexus
lime nexus
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does it make sense now?

marble summit
lime nexus
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hurray

marble summit
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do you mind, if i add you to ask more question?

lime nexus
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suree

marble summit
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appreciate it, man i wanna learn something

lime nexus
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send it thru!

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ill try to help

marble summit
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yes pls, and how do i close this help section?

lime nexus
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OH LOL

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.close

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but it only closes if u type that

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goodluck!!

marble summit
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oki, accept my friend request, ive already sent it to u

lime nexus
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uh okay?

marble summit
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.close

safe radishBOT
#
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safe radishBOT
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cerulean wolf
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is it "valid" to show lim x->inf of sin(x)/exp(x) = 0 by claiming sin(x) will always be in range -1 to 1 for all real input and then that e^-x goes to 0 and since any real "a" * 0 is 0 it's all 0? or some similar reasoning

cerulean wolf
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or would real proof use the Taylor series or something like that

peak estuary
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you want the squeeze theorem

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-1/e^x <= sin(x)/e^x <= 1/e^x

short topaz
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so like if ur doing i.e. a physics/engineering course, that would probs be sufficient

short topaz
short topaz
cerulean wolf
safe radishBOT
#

@cerulean wolf Has your question been resolved?

safe radishBOT
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half briar
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Can we do this together: THere are 4 races in total which have a winner and 10 participants. What are the possible total results if we only look at races won

half briar
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basically after each race the winners we pick reset

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and the order does not matter i guess

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WE got 10 participants so: A B C D E F G H I J

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Basically asking how many possibilities we can build out of those. Like ACDJ for example

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this formula?

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$$\binom{10+4-1}{4}$$

flat frigateBOT
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Jaeger

digital sparrow
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no wait

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as there is a winner

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each race will have atleast 1 participant

half briar
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what

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its each race same 10 participants

digital sparrow
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like you use this one one group might have 0 objects

digital sparrow
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for this ques that is not possible as

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"each race has a winner"

half briar
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yeah? but every time it resets

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next race new outcome

digital sparrow
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so you just subtract the number of "fixed" objects from the top

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in this case 10 + 4 - 1 - 4

digital sparrow
half briar
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they do a race

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one winner

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next race same person can win again

digital sparrow
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no i dont think that is the case

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more like 10 ppl divided into 4 groups with no repetition

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then one winner out of each group

digital sparrow
half briar
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Can be anything like AAAA AABC etc

digital sparrow
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i mean it is kinda vague

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like how are the races conducted?

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and what does "only wins matter" mean

safe radishBOT
#

@half briar Has your question been resolved?

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outer lance
#

Someone help me with derivatives please. Ive been stuck looking at my page for hours because I cannot seem to understsnd

crystal cloud
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send the sum

outer lance
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Both E and F

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For E I understand that it equals to sin (x+y)

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But why isnt the derivative cos(x+y) • y'

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using chain rule

crystal cloud
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no it will be cos(x+y)

outer lance
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But I thought you had to use chain rule and multiply the inside afterwards

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The answer is -1 btw

crystal cloud
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nah

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are u sure

outer lance
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Yes

crystal cloud
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lemme get a paper hodl

outer lance
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I got that

crystal cloud
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i got it

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solved it

outer lance
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ok how pls

crystal cloud
outer lance
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Oh wait im stupid

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I forgot derivative x is 1

outer lance
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I can show you my work but my answer is slightly different for some reason

crystal cloud
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what is the answer

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yeah show me the work

outer lance
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cos x-2sinx2x-2y /2x

crystal cloud
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what

outer lance
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answer

crystal cloud
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can u send a piv

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itll be better pls

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idk if it is correct.

outer lance
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The answer is (cos x- 2sinx2x- 2y) / (2x)

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idk where the 2y or 2x comes from

crystal cloud
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mine is correct

outer lance
crystal cloud
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no i did not

outer lance
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derivative of 2xy = 2y' no?

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where did you get the x and 2y from

crystal cloud
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its 2 dy/dx

outer lance
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He has the right answer idk how

crystal cloud
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no i wrote the positive first and

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then the negative term

outer lance
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Can you show your work maybe

crystal cloud
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mine is correct 😭

outer lance
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well its somehow correct

crystal cloud
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no om

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wait guys

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its aarya lol

outer lance
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Yeah can you show how you got it

crystal cloud
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here

outer lance
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Thats wrong tho

crystal cloud
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u j have to write sin first then thr cos term

outer lance
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is x times dy/dx not just 1?

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because derivative of x = 1?

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why wouldnt 2xy = 2 (dy/dx)

crystal cloud
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it is 1

crystal cloud
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buddy cmon i solved it i dont get what ur cribbin on

outer lance
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Yeah but my answer key says theres a -2y and x somewhere

outer lance
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Ive said this like 100 times

crystal cloud
outer lance
crystal cloud
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OH I FORGOT PRODUCT RULE?

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shit im so so so so sorry

outer lance
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wait so the derivative of 2xy = 2xyy' or what

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Im still lost

crystal cloud
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cuz yall did not use rhe term

outer lance
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Oh wait

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Product rule

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I see it

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I got it thanks

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In the answer there is no negative

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Is there another negative sign im missing for I)?

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i

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also how is the apart of the derivative of sin^4(2-x)^-1 just cos (2-x)^-1

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why wouldnt it be like cos^4 or smt

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Its like (2-x)^-1

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so it would be 3sin^4(2-x)^-1

safe radishBOT
#

@outer lance Has your question been resolved?

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graceful widget
safe radishBOT
graceful widget
#

N1 and N2 are norms

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how do i prove that Cn exists?

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Cn>0

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<@&286206848099549185>

steep lily
graceful widget
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are you doing it now?

steep lily
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Yes, though I might need some time

graceful widget
#

ok im gonna wait for you thanks

plucky elk
flat frigateBOT
#

riemann

graceful widget
plucky elk
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yea that's important to tell

graceful widget
#

ok

safe radishBOT
#

@graceful widget Has your question been resolved?

steep lily
#

(I was unable to figure it so far and I have to go, see my previous advice)

graceful widget
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@plucky elk hello just in case

plucky elk
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if you're not doing anything, i suggest doing it for small n like 1 and 2 to see how both sides evaluate to try to find a pattern

graceful widget
plucky elk
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no

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what

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do your own homework

graceful widget
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but i dont know how to do it

plucky elk
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do you know what p looks like for n=1 ?

graceful widget
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aX

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a real number

plucky elk
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no

graceful widget
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a then

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aX + b

plucky elk
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yes aX+b

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plug that into both sides

graceful widget
plucky elk
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C_n is notation for a constant that depends on n

graceful widget
#

ok

graceful widget
plucky elk
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probably gonna take more than just n=1 to find the pattern

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try n=2

graceful widget
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no i was wrong in my first answer

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a²/3 + ab/2 + b² and the right side it's a²/4 + ab + b²

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i see that it is smaller

safe radishBOT
#

@graceful widget Has your question been resolved?

safe radishBOT
#
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golden granite
safe radishBOT
golden granite
#

How do I know which interval makes it true

lean otter
#

u know multiplying two positive numbers or two negative numbers is > 0. if one is positive and the other is negative then it is < 0

golden granite
#

So you plug in the solutions into the problem above?

hidden gyro
golden granite
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Right

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So is it the top and bottom

hidden gyro
#

no

lean otter
#

ok easier example, (5)/(-3) is < 0 and (-5)/(3) < 0

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but (5)/(3) > 0 and (-5)/(-3) > 0

golden granite
#

ok

lean otter
#

so u need [x+2 <=0 and 4x > 0 ] or [x+2 >= 0 and 4x < 0]. do you see why?

golden granite
#

Because if it’s zero in the denominator then it’s undefined

lean otter
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ok that is also true

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but i meant that n/d <= 0 if [n<=0 and d>0] or [n>=0 and d<0]

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it means that one number is positive (+) and the other is negative (-), so the multiplication is negative (+- -> -) idk if i explain myself correctly

golden granite
#

Yeah I got you

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And if they’re both negative it’s pos

lean otter
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yes

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so basically u need (top >= 0 and at the same time bottom < 0) or ( top <= 0 and at the same time bottom > 0)

golden granite
#

Does that always apply

lean otter
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i think ur not getting how im trying to explain it

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+/- is negative and -/+ is negative

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+/+ is positive and -/- is positive

golden granite
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I know

lean otter
#

okay how would you solve it

golden granite
#

Look at the 2 intervals that result in a positive fraction

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and use those number

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[-2,0)

lean otter
#

oh i didnt see the whole image

lean otter
#

but yes, that happens in [-2,0) because the image says -1/4 <= 0

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so u already know the answer

golden granite
#

yeah

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lol

safe radishBOT
#

@golden granite Has your question been resolved?

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sand garnet
#

How do I find the mean?

safe radishBOT
versed pendant
#

Area/x

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This is the definition of mean, and area is the sum of every y

halcyon dagger
#

thats for discrete

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continuous requires integral

versed pendant
#

Yup. 👍

halcyon dagger
#

int[0,10] (x*f(x)) dx

safe radishBOT
#

@sand garnet Has your question been resolved?

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native robin
#

A ball of mass $m$ dropped from a distance $d$ above a plate attached to a spring with spring constant $k$ compresses the spring a distance $x$.

flat frigateBOT
native robin
#

Derive an expression for x, the distance the spring compresses as a result of the interaction with the ball.

odd crest
#

energy conservation

native robin
#

do i have the right setup here:

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$mg(d+x)=\frac{1}{2}kx^2$

flat frigateBOT
supple shore
#

make a scheme of the situation maybe you will see it better, I don't really understand here

safe radishBOT
#

@native robin Has your question been resolved?

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shy wing
#

Trying to study for my test that's coming up, and on the review this problem came up which is very confusing. It's part of the autonomous equations, but the book and lecture don't really cover too much of it, or what "absent harvesting" means, or what a condition would mean towards the problem.

So what I do know: The logistic equation I have been taught goes by:

dx/dt = kx(M-x)+-h

where k is a constant based on the yearly renewal of the population, M is the carrying capacity, x is the population.

I know generally, expanding out the equation and setting up the quadratic equation is helpful, as I'd want the radical to end up being 0. Now, a few issues. It says absent harvesting, but then it says the lake is opening to fishing. So I'm assuming the equation is now what it is, but +-h, where I am solving for h?

As for y(0), I think that means that when t=0, y=1280? I'm honestly not sure with this one, because the lecture or homework didn't really go over conditional statements.

If anyone knows a good way to explain this problem to me, that'd be greatly appreciated.

raven heart
#

Now, a few issues. It says absent harvesting, but then it says the lake is opening to fishing. So I'm assuming the equation is now what it is, but +-h, where I am solving for h?
Yes, but it's not +-h, it's just -h. h is a harvest rate, it's a rate of fish you're removing out of the lake

shy wing
#

I see, it's specified it's 100% going to be harvesting, so it's -h in this scenario

raven heart
#

then the goal is to see how high you can push h so that the equation still has an equilibrium

#

i.e. what's the highest value of h for which kx(M-x)-h = 0 has a solution ?

#

or to use the notations in the question replace kx(M-x)-h by 0.06y(1-y/3600) - h

shy wing
#

Okay, I see. I went ahead and set everything up

#

Lemme send a screenshot

#

Now is that my answer, or do I have to do something with this answer

#

This is as far as I usually get with this problem

raven heart
#

there's a ton of small errors here and there but you fall on your feet in the end at least

#

also +57 not -57

shy wing
#

Where are the errors

#

Ah I see that now

#

Any other ones other than the small one at the end?

#

Ahh I left the +- sign in as a habit

#

So what I did on the third step of the run is I changed all the signs

#

which is why h comes out at a positive number

raven heart
#

most of these signs don't matter in the end tbf

shy wing
#

Yeah would probably have been helpful for me not to continue writing the +- like that lol and yeah it doesn't matter too much, I just did it to keep the lead term positive

#

Made it look better

#

But anyways, now what should be done?

raven heart
#

you're done

#

gg

#

@shy wing

shy wing
#

Okay, so that's what I thought this entire time

raven heart
#

actually

#

yeah I thought the initial condition didn't matter

#

but it does

shy wing
#

Okay that's the missing link

#

I do not know what the initial condition means in relation to the question

#

I can only assume it just means the initial population at the start of harvest is 1280

raven heart
#

yes

#

the idea is

#

here's your function for some h < 57, you get two equilibrium points (approx 800 and 3000 here)

#

problem is

#

if the initial population is less than 800, what happens to the population ?

shy wing
#

h = 38.7?

#

But if the initial population is less than 800, then the population would be on an incline

raven heart
#

incline ?

#

you're sure about that ?

#

this graph is dy/dt as a function of y

#

so if y is less than 800, dy/dt is negative

shy wing
#

I'm not sure

raven heart
#

well I just told you no

shy wing
#

okay so questions

#

What's h=38.7 in this scenario

#

Oh wait

#

That's probably the answer

raven heart
#

don't look into it

shy wing
#

Okay

raven heart
#

also it's not the answer

shy wing
#

Ah yeah I see now

#

I did my calculation wrong

#

When it is less than 800, it is on a decline

raven heart
shy wing
#

Oh

raven heart
#

the f(y) plot at least

shy wing
#

Okay let me try again

raven heart
#

but you should be able to infer the phase line from that

shy wing
#

Is 800 half-stable

raven heart
#

unstable

shy wing
#

Ahh yes

#

i see it now

#

Originally I did not connect the phase line because I'm used to it being a vertical line

#

But if I start at 0, it is negative, or decreases when it's less than 800, and increases when it is greater than 800

#

which is unstable

#

Is that correct?

raven heart
#

yes

#

so the problem is that if you start your population at < 800, the population will go straight down to -infinity

#

i.e. you don't reach an equilibrium

shy wing
#

Yes

#

So maybe instead

#

This looks like it's in the form of a typical population equation

#

Would this ones equilibriums be 0 and 3800? Or do I calculate them in the quadratic equation

raven heart
shy wing
#

Ahh yes you're right

raven heart
#

but you still want to do something w/ the quadratic equation

shy wing
#

So I need to use the quadratic for the new equilibriums

raven heart
#

yes

shy wing
#

And is this for h=57?

raven heart
#

what is ?

shy wing
#

Sorry

#

In the quadratic equation, am I assuming the harvest rate is what I found?

#

So the radical would be 0?

raven heart
#

we want something more precise than that though

#

I'll increase h a little bit on my graph and you'll see

#

ok h=53.4

#

you still have 2 equilibriums, approx 1400 and 2400

#

what happens if you start at 1280 now ?

shy wing
#

Population is declining still

#

Ooh idea

raven heart
#

yeah and we don't want the population to decline when we start at 1280

shy wing
#

If the population is 1280 at y(0)

#

Would I find h by setting the equation = 0 when = 1280?

#

And then run my quadratic using that harvesting number for that population to find my equilibriums?

#

I see the point now though

#

I want it to be in equilibrium with 1280

raven heart
shy wing
#

Oh

#

So what does that mean

raven heart
#

the quadratic formula gives you the two equilibriums

raven heart
shy wing
#

Okay

raven heart
#

otherwise you end up with a "goes to -infinity" situation

#

the phase line doesn't change very much really, it's just the equlibrium points that move

shy wing
#

I'm just confused on the quadratic formula part

#

h=57 would obviously set the radical to 0 and obviously give me 228/0.12 +- 0

#

Which is reflected in the graph as the vertex

#

1900

#

but that means if I'm at 1280, it's another -infinity issue

raven heart
#

yeah

#

so you don't want h=57

#

you'll want something smaller

#

you want h such that you end up in the 3rd situation

shy wing
#

Oh

#

If 228/0.12 is 1900, then the radical needs to be equal to (1900-1280)^2?

#

so that 228-sqrt()/0.12 is 1280, and then I can find 228+ using that same number?

raven heart
#

228-sqrt()/0.12 is 1280
ok yeah

shy wing
#

I'm sure that's a method, is that the best method to deal with this though?

#

Felt a little weird to me

raven heart
#

"I want 1280 to be between the two equilibria, so I solve for the two equilibria and find the biggest h for which 1280 is between the two"

#

it's not like there's a completely wild step going on here

shy wing
#

Okay

#

Ah wait I did my logic incorrect

#

If 1280/0.12 is 1900, then I simply need the minus term to be 620 but I have to account for the 0.12 on the bottom

#

So the radical needs to be like 74.4

raven heart
#

,calc 0.12*(1900-1280)

flat frigateBOT
#

Result:

74.4
raven heart
#

yea

shy wing
#

So with that, I set up my equation 51984-912h = 74.4^2. Solve for h, and I got that my value of h is 50.930, or 51 fish of harvesting?

raven heart
#

yeah

shy wing
#

Okay

#

Yesss

#

Thank you thank you thank you

#

That was a tricky one but I feel like you helped me understand it

#

I hope you have an amazing rest of your day and I appreciate all the help you gave me

#

🫡

#

.close

safe radishBOT
#
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safe radishBOT
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full quarry
#

Just need someone to verify if I’ve done these correct

full quarry
safe radishBOT
#

@full quarry Has your question been resolved?

full quarry
#

<@&286206848099549185>

full quarry
#

@helpsrs

#

<@&286206848099549185>

#

.close

safe radishBOT
#
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spiral saddle
safe radishBOT
spiral saddle
#

let $f : \mathbb{V} \to \mathbb{V}$ such that $M_{B}(f) = \begin{pmatrix} 1 & 4 & -5 \ 2 & 1 & 0 \ 0 & 3 & 1 \end{pmatrix}$ and let $B = {v_1, v_2, v_3}$ and $B' = {-v_1 + v_2 - v_3, v_1 + 2v_3, v_2 }$ bases of $\mathbb{V}$. Find $M_{B'B}(f), M_{BB'}(f)$ and $M_{B'}(f)$

flat frigateBOT
#

938c2cc0dcc05f2b68c4287040cfcf71

torpid elbow
#

Helpers

#

<@&286206848099549185>

mystic adder
#

e is 2.71 if I'm correct? then you need to calculate it

#

I'm not sure

safe radishBOT
#

@spiral saddle Has your question been resolved?

spiral saddle
#

<@&286206848099549185>

safe radishBOT
#

@spiral saddle Has your question been resolved?

spiral saddle
#

<@&286206848099549185>

spiral saddle
#

<@&286206848099549185>

spiral saddle
#

<@&286206848099549185>

safe radishBOT
#

@spiral saddle Has your question been resolved?

spiral saddle
#

<@&286206848099549185>

final wasp
#

e ≈ 2.71828

#

normally your teachers want you to use either 2.72 or 2.718

tender sleet
spiral saddle
#

help

#

let $f : \mathbb{V} \to \mathbb{V}$ such that $M_{B}(f) = \begin{pmatrix} 1 & 4 & -5 \ 2 & 1 & 0 \ 0 & 3 & 1 \end{pmatrix}$ and let $B = {v_1, v_2, v_3}$ and $B' = {-v_1 + v_2 - v_3, v_1 + 2v_3, v_2 }$ bases of $\mathbb{V}$. Find $M_{B'B}(f), M_{BB'}(f)$ and $M_{B'}(f)$

flat frigateBOT
#

938c2cc0dcc05f2b68c4287040cfcf71

tender sleet
#

idk sry

spiral saddle
#

is oki

spiral saddle
#

\textbf{Property (base changes in the matrix of a linear transformation):}

Let ( B_V ) and ( B'_V ) be bases of a vector space ( \mathbb{V} ) and ( B_W ) and ( B'_W ) be bases of a vector space ( \mathbb{W} ). If ( f : \mathbb{V} \to \mathbb{W} ) is a linear transformation, then:

[
M_{B'W B'V}(f) = C{B'W B_W} \cdot M{B_W B_V}(f) \cdot C{B_V B'_V}.
]

flat frigateBOT
#

938c2cc0dcc05f2b68c4287040cfcf71

spiral saddle
#

like this i think

wild cape
#

this doesnt tell me how M is defined

#

well ik the concept but the order of subscripts isnt universal so i'd like it clarified

#

ah this suggests subscripts go right to left

spiral saddle
#

like we need to derive the change of basis matrix formula for each M i think¡

wild cape
#

ok so how do we use this to find M B'B

#

just an equation, no explicit numbers yet

spiral saddle
#

yes but I dont even know what C is

#

someone said identity matrix but im not sure

wild cape
#

just write it down and compute it later

#

its good write the solution symbolically before computing anything

spiral saddle
#

to write down the formula for M B'B I need to know what C is doe

#

but that is my issue, finding the formulas for the matrix representations

wild cape
#

yes but you can just write down an equation using C

spiral saddle
#

oh ok

#

,, M_{BB'}(f) = C_{BE} \cdot M_{EB}(f) \cdot C_{BB'}

flat frigateBOT
#

938c2cc0dcc05f2b68c4287040cfcf71

spiral saddle
#

like maybe like this but im not sure tbh

wild cape
#

whats E

spiral saddle
#

like standard basis

wild cape
#

V is a general vector space so standard basis is nonsense

#

we only have B and B'

spiral saddle
#

oh right im sorry

#

,, M_{B'W B'V}(f) = C{B'W B_W} \cdot M{B_W B_V}(f) \cdot C{B_V B'_V}.

flat frigateBOT
#

938c2cc0dcc05f2b68c4287040cfcf71

spiral saddle
#

domain and codomain are V

#

,, M_{B_VB'V}(f) = C{B_V B_V} \cdot M_{B_V B_V} (f) \cdot C_{B_V B'_V}

#

oh my, I messed up wait a moment

flat frigateBOT
#

938c2cc0dcc05f2b68c4287040cfcf71

spiral saddle
#

no idea tbh

#

this stuff is confusing as hell

wild cape
#

general tip for math, always try to understand the form of a rule instead of the exact letters

#

i think the best way to understand change of basis is the right to left order of subscripts

#

back to the general rule

spiral saddle
#

what do you mean right to left subscripts}

wild cape
#

change of basis tells us there are two ways to compute f(x)

#

the first way is direct via $[f(x)]_{B'W}=M{B'_WB'V}(f)[x]{B'_V}$

flat frigateBOT
#

𝓡𝓞𝓚𝓔𝓣𝓣𝓞─୨ৎ─❥ ♡ <𝟹❤

wild cape
#

agree?

spiral saddle
#

oh my

wild cape
#

have you seen this property?

spiral saddle
#

I have never seen this no

#

what is it ?

wild cape
#

do you know what [x]_B means

spiral saddle
#

coordinate of x with respect to basis B?

wild cape
#

yes

spiral saddle
#

is this the first way ?

wild cape
#

this property is a generalized version of standard matrix for linear maps R^n->R^m

spiral saddle
#

right to left subscripts?

wild cape
#

ill get to that later

spiral saddle
#

okok

wild cape
#

standard matrix for linear map f:R^n->R^m satisfy f(x)=Ax yes?

spiral saddle
#

sure

#

linear transformation can be expressed as matrix multiplication i think

wild cape
#

but now for f:V->W the matrix product no longer makes sense

spiral saddle
#

mmm

wild cape
#

we compensate by using coordinates

spiral saddle
#

how

wild cape
#

you can see it still roughly follows the form of f(x)=Mx

spiral saddle
#

like for M_{B'_W B'V}(f)[x]{B'_V}

#

what is that with words

wild cape
wild cape
spiral saddle
#

matrix change of basis input basis of domain B' with domain W and output basis B' with codomain V of linear transformation f multiplied by coordinates of x with respect to basis B'

#

something like that?

#

is a mouthful

wild cape
#

my phrasing is more succinct, having all those variables kinda clutters the meaning

spiral saddle
#

like output basis of the matrix representation must match

#

in order to be multiplied

wild cape
#

x is in V so it only makes sense to use a basis of V for coordinates

#

tbh i can restate the rule without the primes, no difference

spiral saddle
#

yes

wild cape
#

the primes only exist to properly state change of basis

#

$[f(x)]{B_W}=M{B_WB_V}(f)[x]_{B_V}$

flat frigateBOT
#

𝓡𝓞𝓚𝓔𝓣𝓣𝓞─୨ৎ─❥ ♡ <𝟹❤

wild cape
#

ok is this clear now?

spiral saddle
#

sorta

#

like is a complex topic

wild cape
#

if its still not fully clear i would go back to these two messages

spiral saddle
#

I hate it the subscripts V and W make everything like 10 times more confusing

wild cape
wild cape
#

but you can do that later

#

ok we're back to this

#

this tells us there are two ways to compute f(x)

#

the first way is direct via $[f(x)]_{B'W}=M{B'_WB'V}(f)[x]{B'_V}$

flat frigateBOT
#

𝓡𝓞𝓚𝓔𝓣𝓣𝓞─୨ৎ─❥ ♡ <𝟹❤

wild cape
#

the second way is indirect via [[f(x)]{B'W}=C{B'WB_W}M{B_WB_V}(f)C{B_VB'V}[x]{B'_V}]

flat frigateBOT
#

𝓡𝓞𝓚𝓔𝓣𝓣𝓞─୨ৎ─❥ ♡ <𝟹❤

spiral saddle
#

bruh

#

wait a secons

#

you modfied the formula??

wild cape
#

i rewrote the RHS using the change of basis rule

spiral saddle
#

LHS aswell

wild cape
#

i didnt

spiral saddle
#

M_{B'w B'v}(f) vs

[f(x)]_B'w

#

like what happened with B'v output basis

wild cape
#

??

spiral saddle
#

ohh you modified the RHS by multiplying with

#

okay that's way better

#

[x]_{B'v}

#

okay now what?

wild cape
#

now this is where the understanding of the rule comes from

#

we apply the effect of each matrix to [x] going right to left

#

and the subscripts guide us

#

the first product is $C_{B_VB'V}[x]{B'V}=[x]{B_V}$

flat frigateBOT
#

𝓡𝓞𝓚𝓔𝓣𝓣𝓞─୨ৎ─❥ ♡ <𝟹❤

spiral saddle
#

right to left

wild cape
#

the second product is $M_{B_WB_V}(f)[x]{B_V}=[f(x)]{B_W}$

spiral saddle
#

okay

flat frigateBOT
#

𝓡𝓞𝓚𝓔𝓣𝓣𝓞─୨ৎ─❥ ♡ <𝟹❤

wild cape
#

the last product is $C_{B'WB_W}[f(x)]{B_W}=[f(x)]_{B'_W}$

flat frigateBOT
#

𝓡𝓞𝓚𝓔𝓣𝓣𝓞─୨ৎ─❥ ♡ <𝟹❤

wild cape
#

this verifies the indirect way of computing f(x)

#

remember, the understanding of change of basis is the right to left effect of matrices guided by subscripts

#

use this whenever writing down the appropriate change of basis for a problem

wild cape
#

@spiral saddle

wild cape
wild cape
spiral saddle
#

ok

#

I will come back tomorrow to finish this, thank u fir the definitions

#

like I feel so tired I was falling sleep

wild cape
#

for example $M_{B'B}(f) = C_{B'B} M_{BB}(f) C_{BB}$

flat frigateBOT
#

𝓡𝓞𝓚𝓔𝓣𝓣𝓞─୨ৎ─❥ ♡ <𝟹❤

wild cape
#

no prob

#

when you wake up, please go over all of this convo to make sure it sticks

wild cape
robust river
#

I also tried to explain that stuff yesterday

#

Explaining is harder than it seems 😅

safe radishBOT
#

@spiral saddle Has your question been resolved?

safe radishBOT
#
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#
Available help channel!

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Ask your math question in a clear, concise manner.
Show your work, and if possible, explain where you are stuck.
After 15 minutes, feel free to ping <@&286206848099549185>.
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• Be polite and have a nice day!

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split fulcrum
#

Confused on what to do next

safe radishBOT
split fulcrum
#

,rotate

flat frigateBOT
safe radishBOT
#

@split fulcrum Has your question been resolved?

lime nexus
# flat frigate

use ref sheet for normal distribution, in their 30s is essentially between 30-40

#

notice how its also between z score of -1 and 1

#

also hi again lol

#

and in 40s would be ppl between age of 40-50 which if u keep drawing the curve itll be z score of 1 to 3

split fulcrum
#

😭 this normal distribution shit killing my confidence

lime nexus
#

NOO U GOT HTHS

#

BEELIVE

lime nexus
rich elm
#

universal hsc suffering experience

#

@split fulcrum u got this

lime nexus
rich elm
#

yeh

lime nexus
#

ohhh nice

split fulcrum
rich elm
#

do you have a routine/working out process for finance questions?

#

they tend to fall similar to each other in some way or the other, being AP or GP mostly

#

dont ask me about FV and PV stuff, i just guessed those questions when i did adv last year

#

(bad student)

split fulcrum
split fulcrum
lime nexus
#

remember the rules

#

between -1 and 1 is 68%

#

-2 and 2 is 95%

#

and so on

rich elm
lime nexus
rich elm
#

z score tells u how many standard deviation a particular 'event' is from the mean

lime nexus
split fulcrum
#

so like

#

1 standard deviation from the mean is

#

36?

lime nexus
split fulcrum
#

like 36 years old

lime nexus
split fulcrum
#

but the people aged between 30-40s isnt that 10 standard deviations but the normal distribution curve only goes to like 3 standard deviations

lime nexus
#

one standard deviation = 5 year difference

#

so ig 10 year difference is 2 standard deviations away from each other (technically)

rich elm
#

but they are respectively 1 standard deviation from the mean

#

1 z-score = 1 standard deviation

#

z-score could be thought of as the 'unit' for how many standard deviations

split fulcrum
split fulcrum
#

so 30 to 40 is 68%?

lime nexus
#

yuhhh

split fulcrum
#

so um how do we use this to help us?

lime nexus
#

since we know now that ppl in their 30s makes up 68% of the ppl in the league

#

u can use that fact to find the exact amount of ppl in the 30s now right?

#

we know the total is 10000 ppl

#

and 68% of that is ppl in their 30s

#

so what do u think u can do to find the exact amount of ppl in their 30s?

split fulcrum
rich elm
#

si

#

👍

split fulcrum
#

6800 people in their 30s

#

to get from 40 to 50 thats 2 standard deviations?

lime nexus
split fulcrum
#

so from the mean its 3 std

lime nexus
rich elm
#

think about it geometrically

#

draw out the normal distribution curve if need be

#

think about which part of the graph is inclued in the 40-50

#

range

split fulcrum
#

uh

lime nexus
split fulcrum
split fulcrum
lime nexus
#

is it 50 years after the 40?

lime nexus
# lime nexus

notice this graph here (its on ref sheet) the 0 essentially means that at thay point it is the mean, the 1 from 0, means its one standard deviation to the right, ig u can think of the negative as in the other direction, its one stdanrd deviation to the left, the 2 means 2 standard deviations to the right of the mean and so on yeah?

split fulcrum
#

yeah

#

i just dont get why from the mean, 50 years isnt 3 standard deviations

lime nexus
split fulcrum
#

so from the mean to 50 years is 49.85% of data right?

#

because you halve 99.7

lime nexus
#

the 2nd standard deviation should be 45, not 50

#

as each stadnard deviation is 5 years right?

split fulcrum
#

ohh

#

yeah

lime nexus
#

so if it is 40 years at the 1st stdanrd deviation, u need to add 5 to get the the 2nd stadnard deviation right?

#

and another 5 to the 3rd

split fulcrum
#

yes

lime nexus
#

so far so good?

split fulcrum
#

yeah

lime nexus
#

so first of all we know that terms 6800 ppl in their 30s

#

we want to find how many ppl r on their 40s

#

with the info we have rn we are able to calculate the percentages of ppl in their 40%

split fulcrum
#

idk if this is right

#

,rccw

flat frigateBOT
lime nexus
#

take a look at the curve and tell me between which deviations are ppl aged in their 40s r between

lime nexus
split fulcrum
#

15.85%

lime nexus
#

yessss

#

now with that

#

u can use it to find the ppl in their 40s yeah

#

which isssss

#

u tell me

split fulcrum
#

1585 people

lime nexus
#

yuhhh

#

now back to the qn

#

we want to find the difference in amount of ppl right

#

so what do u do now?

split fulcrum
#

subtract 6800-1585 = 5215

lime nexus
#

yuhhh

#

woop woop

#

i think thays the answer

#

dont ahve a calculator on me rn

split fulcrum
#

@junior smelt hello devilish

lime nexus
#

eating dinner

split fulcrum
#

ye it is

split fulcrum
lime nexus
#

shhhh

split fulcrum
#

so part B how do i do that

lime nexus
#

what do u notice about it

split fulcrum
#

is this just the portion of people who are 50 or over technically

lime nexus
#

(i got this part of the qn wrong before its okay)

split fulcrum
lime nexus
#

but

#

it is

#

but isnt

split fulcrum
#

what 😭

lime nexus
#

read it

#

very carefully

split fulcrum
#

percentage of people aged 40 or over who are also 50 or over

lime nexus
#

im not a fan of thr wording

split fulcrum
#

what does this mean

#

do they want me to find like

#

the number of people in between

#

or something

lime nexus
#

nope

#

its like

#

out ouf the people whos aged 40+, how many of them are 50+

#

(dont be like me who just thought i just needed to find how many ppl are over 50+) and divided it by 10000

lime nexus
split fulcrum
#

but thats just the amount of people who are 50+ cuz technically theyre 40+ 😭

lime nexus
#

the question is basically asking, find the % of ppl aged 50+ but u divided by by the % of ppl aged 40+

lime nexus
lime nexus
#

does this kinda make sense

split fulcrum
#

yes and no

lime nexus
#

which part doesnt

split fulcrum
#

so it wants to know like

lime nexus
#

ill try to explain

split fulcrum
#

out of the people who are 40+ it wants to know how many of those 40+ people are also over 50+

lime nexus
#

yessss

#

so note

lime nexus
split fulcrum
#

ya i realize now

lime nexus
#

yeyeye

#

bro they put this qn in my trials but changed the numbers

#

and part b

#

i got a 0

#

bc i just thought isnt it just the amount of ppl over 50

lime nexus
#

so sad

#

anyways

lime nexus
#

try giving it a go

split fulcrum
#

so people aged 40 or over have z>1

lime nexus
#

correct

split fulcrum
#

so that means that

#

34% of people have z>1?

lime nexus
split fulcrum
#

actually

#

no im not sure

lime nexus
split fulcrum
#

is it 16%

lime nexus
#

mhmm

#

do yk why its 16

#

do i assume u get 34 from dividing 68 by 2?

split fulcrum
#

yeah

lime nexus
#

remember its only 68% if its between -1 and 1 right

#

so if u half it

#

only half of it is 34% ie from 0 to 1 or -1 to 0 is 34%

#

notice how from 0-1 it is indeed 34%, but that saying its not z>1 right?

split fulcrum
#

yeah

lime nexus
#

its z<1 or more specifically 0<z<1

#

odes that make sense?

split fulcrum
#

ye

lime nexus
#

yess

#

another way is that

#

0 is the middle point

#

everything to thr right of it is 50%

#

everyone to the left of it is 50% too

#

overall making up 100%

#

so if yk from 0 to 1 is 34%

#

z>1 is the rest of it

#

u can just do 50-34

#

to get z>1

split fulcrum
#

ohhh okay

#

true

#

that makes sense

lime nexus
#

yayy

lime nexus
#

js longer

#

time is precious in the hsc!

#

anyways

#

we now know that 16% of the total makes up z>1 aka ppl aged 40+

#

what would u do next?

split fulcrum
#

i multiply it by 10000?

#

so 1600 people have z>1

#

or are 40+

lime nexus
#

yes and wha would that number mean

#

oops

lime nexus
lime nexus
#

u got one part done

#

so now we need to find how many ppl are >50 right?

split fulcrum
#

yeah

lime nexus
#

ur nearly there!

split fulcrum
#

so we know like

#

there are 1585 people in their 40s

lime nexus
#

yeah?

split fulcrum
#

and there are 1600 people who are over 40

vale oriole
#

lock in

split fulcrum
vale oriole
split fulcrum
#

stfu i am

#

im doing

#

stats

vale oriole
#

lock in

#

🔒 in

split fulcrum
#

ur 4u exam is on monday too

#

u lock in

split fulcrum
# lime nexus yeah?

does that mean i can take the inbetween of people over 40 and people who are 40

vale oriole
#

AmongUsTwerk lock in pls

split fulcrum
#

okay wait let me draw a diagram

digital sparrow
lime nexus
lime nexus
split fulcrum
#

like if we can subtract this difference