#help-26
1 messages · Page 152 of 1
to get a more rigorous proof you need a much more rigorous statement to prove in the first place
Where would you like more rigor?
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is this correct?
re-check implicit differentiation
I am not sure what youre referencing specifically
${2x\frac{dx}{dt} + 2y\frac{dy}{dt} = 0}$
:D
this should be the correct way to implicitly differentiate, yes?
try subsituting this again
does that change the answer?
@old fox Has your question been resolved?
:D
what do i do next?
${\frac{dy}{dt} = \frac{-\frac{3}{4}}{\sqrt{3}}}$
:D
${\frac{dy}{dt} = -\frac{\sqrt{3}}{4}}$
:D
@old fox
7.5?
@finite storm
could u show how
but its 10 feet away
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hello,
how can i find the probability than some event with probability p occurs more than 5 times in n tries ?
I looked online, i found a "choose" formula with factorials but i dont think it works
there is a way to calculate it manually but assuming you dont need to
i did this times (p)^5 * (1-p)^5
Binomial Calculator computes individual and cumulative binomial probability. Fast, easy, accurate. An online statistical table. Sample problems and solutions.
you can use binomcdf
im trying to implement the formula into a google spreadsheet tho
Calculates the probability of drawing a certain number of successes (or a maximum number of successes) in a certain number of tries given a population of a certain size containing a certain number of
ah yes
ty hahaha
for "prob sucesses" it wants probability for 1 event right
okit does
what is the diff between binomial cumulative distribution and binomial distribution.
if you use the cumulative one
it gives you the probability of x successes or less
if you dont use cumulative then its just the probability of exactly x
whats up
its saying theres a higher chance to hit 5 out of 6 than 5 out of 30
this is obviously not true but i'm not sure where you are going wrong since i can't see what you input
=1-if(J13>5,BINOMDIST(5,J13,A$22,FALSE),0)
j13 is num trials
a22 is probability
a22 in this case is 0.95
ohh
well in this case
actually itrs true
you have a higher chance to hit exactly 5 when you are only doing it 6 times than exactly 5 when you are doing it 30 times
because you would expect more than 5successes if you are oding it 30 times
how can i tell it to include 5 or more sucesses for this formula
maybe i should do 4 with cumulative ?
yes exactly
ok
and one minusthat
like this or diff?
uhh
still similar issue
the one highlighted is 6
6 num trials
(its rounding to two decimals but i would have imagined that theres a better chance to hit >5 with more num trials)
i think its still solving for exactly 5 trials / exactly 4 or less
but i need it to solve for 5 or more
actually lemme try smth
nvm i think solving for exactly for or less but not doing 1- it is the same as what im lookign for
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Is it possible to have a linear transformation T and linearly independent vectors u1, u2, u3 so that T(u1), T(u2), and T(u3) is a linearly dependent set?
sure
send them all to zero
if you have linearly independent vectors you can freely choose what you want their images to be
and a linear map fitting that will exist
i said it was possible and gave an example but my instructor said my answer was entirely incorrect
so i'm just very confused
well then your example was probably incorrect
or you misread the question or something
!original
Please show the original problem, exactly as it was stated to you, with the entire original context. A picture or screenshot is best. If the original problem is not in English, then post it anyway! The additional context might still be helpful. Do your best to provide a translation.
and show your work
I have no idea what your example is supposed to mean
I mean sure
it's not clear
but how is that relevant
LOL
btw, dont use arrows instead of =
messed up the order for the matrices when i originally wrote them but this was the idea
wait
i should have just sent them all to 0 yeah
even with labelling stuff as x, A and b I still have no idea what you are going for
a linear transformation is Tx = Ax
i just show an example that turns linearly independent vectors into independent vectors
DEPENDENT*
well and what are your three vectors u1,u2,u3?
i intended it to be this
OH
i see
ok ok
so if i did Au1, Au2, Au3 separately and then showed these three VECTORS were dependent, would that have worked?
yes
One last thing, I received partial credit for this other question in the same format. How could I improve this explanation?
partial credit is generous for that
if u1,u2,u3 are linearly dependent, then there exist coefficients c1,c2,c3 not all zero with c1u1+c2u2+c3u3=0
but then also c1Tu1+c2Tu2+c3Tu3=0
could you rephrase? i'm having a hard time parsing it
He used the definition of linear independence
i understand the first half now because if the only solution for Ax = 0 is the trivial then it's independent
i dont understand this part's relation
is the ^ just saying that the linear transformation doesn't change anything?
since that's the definition of a linear transformation basically
yes
If you apply T on both sides
and apply its properties
T(0) = 0
T(av1+bv2) = aT(v1) + bT(v2)
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help
had to find taylor serie and interval
found the taylor but i dont know how to continue for interval
Interval as in where the series converges?
yes
So for clarity, it’s the one on the bottom left?
yeah that the taylor i found
how do you find the radius first of all
how do i find the radius without the the interval ? can i ?
well yeah, there's a formula for the radius of convergence
So since it’s written as a power series a good way to start is to examine the coefficients using something like the ratio test etc
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Iam a starting with multi variable calculus and i need to cover these topics -Functions of two variables-limits and continuity-partial derivatives –total differential-Jacobian
and its properties. any youtube channels for this topic ?
I think Organic Chemistry Tutor has a few videos on Calc 3, which will cover limits of functions of 2 variables and partial derivatives.
Dr. Trefor Bazett also has a playlist for Calc 3 and I think it covers essentially all the topics you've requested, although you could skip through the curvature stuff for curves if you don't need it.
And Paul's Online Notes covers all those topics in written format which can help getting another point of view on the subject if you're primarily learning from a textbook.
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help
Trying to solve by showing the sequence of partial sums is uniformly convergent
wanted to know if my way of finding n is legal
@neon iron Has your question been resolved?
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Help with strong induction problem
I’ve been working through this problem and i don’t really know what to do.
I understand the base b notation and everything, but i can’t seem to find a way to prove it for n + 1.
I already know the inductive hypothesis in which i assume all k numbers with k <= n can br written in base b.
I’ve tried some extensions of the proposition but nothing really proves the induction
Any help would be appreciated
My work is messy though i’m not sure it’ll help
Once you write,
$n = \sum_{i=0}^{l-1} k_{i} \cdot b^{i}$
Just add 1 to the both sides and then manipulate the RHS to take the expected form.
Anonymous
I have totally forgotten Latex. Excuse me.
Anonymous
Two separate cases.
Yeah thats in the statement as the l numbers are up to b - 1 and l is bigger than 1
So thats true for numbers in base b
No. No. You are misunderstanding.
Ah that has to be a condition to be proven true
You shall have two cases as in,
case 1 : $k_{0} = b -1$
case 2: $k_{0} < b-1 $
Anonymous
I dont see how the two cases could be applied to the sum? Sure they are there but i cant really see the implications
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hello, for this question, if it says « divisible by x » is it correct to assume that the eqn = 0 when x = 1?
otherwise i am not sure how to proceed with the question
no. divisible by x means expression = 0 when x = 0, not x = 1
thanks mate
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✅
nevermind ive just run into another problem
if
x=0 then eqn = 0
so r = 0
hollon lemme check if i did something wrong with the working at the side
yea i just realised 
im blind sorry
okay i think i should be able to do the qn without any problem now,,,
thanks mate
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@bleak wedge Has your question been resolved?
No
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third line to 4th line how did they transform the numerator
from this
to this
wont the second one have sqrt(S_xx) in the denom of the upper fraction
Im tripping idk
wait nvm
ignore
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How do i find the domain and range of y = tan^-1(tanx) ?
the domain of your function should be when tanx is defined, while the range of it is from −π/2 to π/2 rad
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Why did they go with that interval
instead of .01 to .025
it doesnt even look like its gonna be between (.025, .05)
so why .02 to .05
wait wtf the exact valye is 0.0354????
ai now Im lost
oh wait wtf (forgot to ultiply the bounds by 2)
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Let x(t)=h(t-k) and y(t)=x(2*t) then what is y(t) in terms of function h whether h(2(t-k)) or h(2t-k) i am looking for proper explanation...
The second one
x(2t) means: wherever you see t in the expression of x(t), replace t with 2t
so you mean the second one
x(...) = h(... -k)
put 2t in there
h(2t - k)
The second one
x(2t) means: wherever you see t in the expression of x(t), replace t with 2t
Wait i recently asked this question if y(t)=x(2t) then wht is y(t-k) the answer tht i received was x(2(t-k)) rn iam little bit confused
@devout bridge Has your question been resolved?
we're doing the opposite now
y(...) = x(2(...))
so if you plug in t-k
y(t-k) = x(2(t-k))
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Okay so I have a square, I need to find the perimeter, area, and side length, but I only have the diagonal, which is 26m. How do I find them?
that's great this means d = sqrt(2)x
you can now calculate the perim as 4x and area as x^2.
you don't have to write decimals you can keep it in terms of sqrt(2)
don't use calculator
d² = 2x²
x² = (1/2) d²
x² = (1/2) • 26 • 26
x² = 13 • 26
x² = 338
x² is the area right
yes
Okay well that leaves me with one answer
Because it's multiple choice
Thanks
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Wait on the 3rd line where does the 2nd sin^2(theta) go?
LCM i.e. similar to
1/2 + 3/2 = 4/2 = 2
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is there a straight forward way to find the minimum value of this
like if you do some algebra based on the partial derivatives it works, but what if you can't think of the algebra tricks used/factorizations
(please ping me)
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@silk tendon Has your question been resolved?
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is there any tricks to solve identities?
trig identities?
yes
Yeah, practice
the grade 11 one is already hard when i learned it and advance function one is even harder
Give an example and explain your thought process
Like this one
I think you have to apply the formula of tan alpha and beta
You can search this formula on internet and then apply the formula on left side
hm ok
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I have no idea where to start with this problem :(
me neither
@narrow kite Has your question been resolved?
<@&286206848099549185>
Do you know that every wave can be decomposed into the sum of sine and cosine waves?
Yea it says that below the middle c is the sum of the harmonics
they are all sine waves but I dont know where to start in figuring out the numbers
a sin(Ax) means a is the amplitude and A is the frequency (It is called standard form if you are interested)
amplitude is easy to guess from the graph
It means the highest value of your sine function in this case
no yea, I just cant seem to understand how to figure out the preiods
because they arent nice numbers
periods*
like the amplitude for the graphs are 3 1 1 respectivly
for asinAx+bsinBx+csinCx
but I dont know waht the A B and C values are
and I dont know how to figure them out
Well, we can guess by counting the number of oscillations over some time interval
ohhhhhh
that makes so much more sense
ok well we have 0.008
and yellow oscillates 2 and a tiny bit times
green 4 and a bit times
and blue 6 times
bit the oscillations finish slightly before 0.008 so how do we deal with that
is this what you mean btw @prime flame
Yeah, but the number is quite ....
And I think in some cases using period is easier
how would you figure out the period then
Then you can compute frequency by 1/period
period is the number of time the wave need to complete one cycle
Yea I got that, but how do I figure out how much time it takes when the graph doesnt show the exact number? Do I guess with the number of ocsilations?
Example, for the yellow wave, if you choose a point at x = 0 then the wave completes one cycle at a point a little bit smaller than 0.004
But it is not 0.004 as they have hinted
So I am choosing another point
Is this all of the information?
this is all of the info
Ok then it is a guessing game then
ok so we know yellow oscillates 2 times in 0.008 seconds
this means that one ocillation takes 0.004 seconds
1/0.004
right?
Sadly, it is not that
it is a little greater than 2
so would we just guess?
how do you convert the number of oscilaltions to the period of the graph
wait nvm i got it
frequency = number of oscillations/time and period = 1/frequency
and we need frequency
f(x)=sin((2pi/T)x)
And damn looks like the frequency here is not an integer
yeaaa
well, it looks like its kinda 0.758 is one period
sorry not one period
the end of the graph
like I got that
so the colours match up
btw do we need to be exactly, tho?
surely there is a way to figure out exactly what the period is though instead of guessing
I have no idea :(
wait wait
could we use simultaenous equations?
What do you mean?
one sec, im writing something out
im not sure if itll work but im just going to try anyway
wait nvm it wont work
im just trying to wrap my head around how we can figure the periods out exactly
If it is a real number then we can't figure it out exactly by eyeballing the graph, tho
Yea, im worried that theres just some trick that im missing
Try to read through your book, again 😂
trueee
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hi
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how do i find the domain & range of -2y+4=1-5x ? i rewrote it in slope intercept form y=5/2x+3/2 , does it matter what number i plug in for x
You say that because it's linear function, it's domain is ] -\inf, \inf [ .
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shouldn't the t be in the denominator position?
artemetra
but in this case they put it there to make Q/t = power, which you are given
aha
you aren't given Q or t but you are given Q/t
makes sense
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So you have equation of a plane in form Ax+By+Cz=D with a defining point P with x, y, and z as 0,0 on that plane, how would it be determined an x and y value on plane relative to P? This is in 3d space and all numbers are real and finite. To start I define a plane by 3 points and get said plane formula. If it helps this is in a 3d space with a view point and a view plane defined. How would I get xyz back from this? X E.
Sorry I have many questions, feel free to ask if you want to know anything. X E.
This is for finding centroid of a 3d planar shape in case that helps. X E.
If anyone knows what this is called might help too. X E.
3 points in plane are defined with x, y, and z known. X E.
<@&286206848099549185> Sorry I do this. Only one call this time, sorry about before. X E.
Is there a way without sine and cosine constantly? Trying for as exact as possible. X E.
@median moat Has your question been resolved?
https://mathworld.wolfram.com/PolygonCentroid.html https://mathworld.wolfram.com/PolygonArea.html X E.
The positions of the geometric centroid of a planar non-self-intersecting polygon with vertices (x_1,y_1), ..., (x_n,y_n) are x^_ = 1/(6A)sum_(i=1)^(n)(x_i+x_(i+1))(x_iy_(i+1)-x_(i+1)y_i) (1) y^_ = 1/(6A)sum_(i=1)^(n)(y_i+y_(i+1))(x_iy_(i+1)-x_(i+1)y_i), (2) where A is the polygon area and x_(n+1)=x_1 and y_(n+1)=y_1 (Bourke 1988, Nürnberg 2...
The (signed) area of a planar non-self-intersecting polygon with vertices (x_1,y_1), ..., (x_n,y_n) is A=1/2(|x_1 x_2; y_1 y_2|+|x_2 x_3; y_2 y_3|+...+|x_n x_1; y_n y_1|), (1) where |M| denotes a determinant. This formula is sometimes written in an abbreviated form as A = 1/2|x_1 x_2 ... x_n x_1; y_1 y_2 ... y_n y_1| (2) = 1/2|x_1 y_1; x_2...
Those are 2d formulas, just how to do 3d?
I guess ping me if you have an answer. X E.
I have this 3d shape projected to a 2d view plane, would centroid in that 2d exactly reflect 3d centroid?
https://mathworld.wolfram.com/GeometricCentroid.html Found this, does this help?
The centroid is center of mass of a two-dimensional planar lamina or a three-dimensional solid. The mass of a lamina with surface density function sigma(x,y) is M=intintsigma(x,y)dA, (1) and the coordinates of the centroid (also called the center of gravity) are x^_ = (intintxsigma(x,y)dA)/M (2) y^_ = (intintysigma(x,y)dA)/M. (3) The cent...
Should I ask a new question? I really want to know how to find centroid of a 3d planar shape, x, y, and z. X E.
By centroid I mean if you defined all points in a shape then their average as would be. X E.
http://mechanicsmap.psu.edu/websites/A2_moment_intergrals/A2-3_centroids_3D/centroids3D.html I don't understand integrals but if someone wants to explain this feel free. X E.
What do I do since it has been an hour and a half?
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how the fuck do you do this tech free
change the bigger division bar into multiplication
so $\frac{\pi}{3} * \frac{1}{\pi}$
AwesomeRat
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is this math correct?
looks fine
@formal peak Has your question been resolved?
Where does the negative sign come from here?
ooh nice catch
(also the integral limits, not entirely happy with them personally
)
Isn't that the usual Laplace form?
(as in, from the picture taken, the integral limits would be affected and changed)
oh shit yea thanks
how so
im not like too experienced with laplace im doing this for a highschool assignment
For any integral substitution, you wanna find out what happens to u when t = 0 and as t -> inf
so the lower limit would be -a?
wouldn't that change the laplace form
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It would as is, but also worth checking how your function f is defined, as likely you have it restricted somehow
.reopen
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how could i define it to make it work
could i assume that f(u), will be zero if u is less than 0
Well, usually you have your Laplace transform defined for functions from the positive numbers to infinity, so likely your f isn't necessarily defined for negative numbers, but usually you choose it to be zero yes 
alright
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Translation: ABCD is a square. ED = 3√2m, calculate NC*
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I'll tell you if you can beat me in a 1v1 clash royale
tell me your ID
havent played in a bit
hol up lemme re download the game]
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I guess you gotta brush up on your log properties alone
LMAO
don’t forget to share the result
thx
so log(a^b) is the top left box
and by log rules it equals
blog(a)
1 sec
k
and the top middle box is log(ab)
which by log rules =log(a)+log(b)
so you want
blog(a) < log(a)+log(b)
agree?
yes
and the third in the top row is
log(a/b)=log(a)-log(b)
so what you really want is
blog(a) < log(a)+log(b) < log(a)-log(b)
okay actually now im confused because looking at your thing it
it says we're increasing from left to right
but also increasing from top to bottom
but both can't be true
is what i thought
but i guess not
every combo i try on one side doesnt work on another
yeah cause it is made wrong
look at this
circle in green is the same thing
if the one to the right in top right is bigger
then how could the one in the middle be simeltaneousy bigger and smaller
Oh nevermind I see, we are allowed to use different numbers in each box
Okay let's restart
alr
yes
log(cd)
is top middle
=log(c)+log(d)
log(e/f) is top right
=log(e)-log(f)
all by log properties
and you want to pick a,b,c,d,e,f from 0 to 9 such that
blog(a) < log(c)+log(d) < log(e)-log(f)
Understand?
kind of
Let's pick b=0
then
log(a^(b))=log(a^(0))=log(1)=0
So it doesn't matter what we pick for a, if we pick b=0, the top left box is 0
that's good because we want it to be smaller than the other boxes
right?
wouldnt we want top left to be smaller tho?
okay so we've used 0 now in a blue box
now let's do like
2*1
so 2 in the red box, 1 in the blue box
for the top middle
log(2*1)=log(2)+log(1)=log(2)
so far so good since 0<log(2)
and now we've used 0, and 1 in blue boxes, and "a" and 2 in red boxes
yep
now for the third lets use 5 in the red box and 2 in the blue box
then log(5/2) = by log rules =log(5)-log(2)
but it is actually more obvious to just simplify it to
log(2.5) to see that it's bigger than log(2)
so then we have in the top row,
0< log(2) < log(2.5)
and we've used 0, 1, 2 in the blue boxes, and "a", 2, 5 in the red boxes
yes
so far so good?
I'm going to retroactively change my choice of 9 to 5
nothing else changes, but it just saves us the bigger number
and it works out the same
ok that works
let's continue down the right side
so right middle box
we'll use 3 in the blue and 1 in the red
so
log(3*1)=log(3)
log(2.5) < log(3)
so far so good
and again noting what we've used:
0,1,2,3 in blue boxes and 1, 2, "a", 5 in the red boes
to be clear we're leaving "a" as a variable because either way it'll end up the same right?
yes, our choice of "a" so far affects nothing so we might aswell leave it to the end and pick whatever works
let's go to the left side going down now
our top left box was
log(a^0)=log(1)=0
so we want something bigger than 0
let's do 3 in the red box and 4 in the blue box
log(3*4)=log(12) > 0
so now let's write again what we've used:
0, 1, 2, 3, 4 in blue boxes and 1, 2, 3, "a", 5 in the red boxes
we need the bottom left corner to be bigger than log(12) now
ah damn looks like we're stuck
bottom left is what gets me
k
yep we back
the 1 in the middle is kind of important
First of all, we can't have a 0 as any of the multiplication boxes
since log(0) is undefined
right?
yes
Which means in those multiplication boxes, we need the top middle, and left middle ones, to be less than 1, and be multiplying two numbers larger than 0
so they have to be 1*2 and 2*1 in whatever order you like
since log(3) > 1
and so is anything greater than 3
oh wait this is log base 10
bruh
I've been treating it as natural log
whatever this still should work
ah ok
austin my mental health sir
whatts up sir
so now when we're picking for the blue boxes in the denominator, we want these to ideally be small as possible
so we pick 3 and 4
and now in the red boxes for the numerators, we need x/4 > 2 and y/3 > 2
so x has to be 9 and we'll let y=8
alr
so now it isn't too hard to fill in the rest
I ended up going with this
but I'm sure you could also fill it in yourself from this point
🫡
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yours is correct
he calculated a weird expression for it
his expression gives each one of the outcome twice
to get each once you gotta substitute n = 2k
you would then get $\theta = (4k-1)\pi$ which is the same as your expression but delayed by one, if you put n+1 in this expression you will get $\theta = (4k+3)\pi$
Mohamed Mohsen
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hello, im doing e-maths and im not too sure how to start with this
when i check the answers, i dont know where 30cm² comes from
maybe the rectangle they drew was 6×5 cm^2
oh
oh yea i needed to measure the square they gave me 
sorry for wasting your time
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you didn't waste time, it's all good
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how does one find a non-bashing solution?
that's all you can do
well i wouldn't say that
hmm
listing out everything is very effective way to do this problem tbh
https://mathworld.wolfram.com/PartitionFunctionP.html partitioning n into k elements is a particularly hard problem. However there is some nice recurrence on it
but yeah listing is probably the best
note: this isn't quite the same as the problem but similar to some extent
pretty much is if you say at most k or something
interesting but ig listing is the easy way out
there is this longgggg formula you can use
💀
P(n,4) is the partition of n parts, where the largest number is 4
but this is equivalent to your definition i think
is it?
list the parts as rows, there are 4 columns (largest is 4)
so we are just counting the columns instead of rows
ok fine
so you substitute n as 0?
n is the number you are partitioning, in your question you are trying to find how many ways to partition 14 into 4 parts: P(14,4)
but this is off topic, but partitioning is a interesting subject if u wanna look up
bro this solution isn't even right
ans is 23. it misses the case (3, 3, 3, 1)
LOL i got 23 with a generating function solution and have just been getting gaslit for the last 10 minutes trying to figure out what i was doing wrong
crazy...
should be 14 mb, edited
though i was getting 23 with a simpler one before and this was supposed to be an alternative
oh yahh
crazy you spotted the exact missing case
@pseudo jetty multivariable generating function
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this also tells you how many solutions if there are only 3, 2, or 1 variables in the problem
what was the simpler one? prod 1/(1 - x^i)
not quite
maybe it wasn't that much simpler lol. i'm not sure how you would track at most 4 parts with prod 1/(1 - x^i) though
that was the purpose of the variable y in what i posted above
oh interesting
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It says
Drawing one and not replacing and then drawing another is the same as drawing two at the same time
Isnt drawing 2 whites
6/9 x 5/8
ok but then for the second one?
it’s 5/8 like usual
not quite
the probability of drawing two whites when you already know the first one is white is 5/8
so i pick a button out of the bag, show you that it’s white, and then we calculate the chances of the second one
ahhh
how would i find the probability of drawing two whites in the first 2 picks
Is it
6/9 x 5/8
yes
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I don't really know if this is even the right discord for this because it's partially related to biology. But does anyone know how long it would take for a population of 250-500 people reach 1,000,000?
@south narwhal Has your question been resolved?
As normal humans would. Nothing is stopping them, such as environment.
Because of the vagueness I’m gonna assume you’re looking for a very rough estimate. To do this you can model the behavior according to an exponential model, and so whatever “as normal humans would” means I would start by figuring out a number on that by googling or just guessing I suppose
I think human growth rate has never gone over 2% per year. But it's vague because I don't need a pinpoint answer, and also because it's based on a story where a village of around 500 people have to repopulate a planet. I want to get an idea of how long it'd take to reach the first million if there were no hardships such as survival placed on them.
are all 500 able of procreation
A very simple model would be something like $P(t) = C r^t$
Aslan
Yes.
Where t is say amount of years, and r is that percentage you mentioned, so like r = 1.02 for example
And C here is the starting population
Which was around 250-500 according to you
Yes.
So what you wanna do with this simple model in order to figure out the number of years it takes for P(t) = 1 million, is just to set up it as an equation and solve for the unknown amount of years t
Unfortunately math left me a long time ago. Is this a forum more teaching how to find the answer rather than giving the answer itself? If so, I apologize.
𝐺=𝑟×𝑁×(1−𝑁𝐾)
alternatively you could use this formula for a logistical growth if your saying as population grows resources are scarcer the need to populate drops
by the time it reachers a million
It’s recommended we try and guide you through the answer but in this specific scenario it’s really not that serious so if you’re just looking for an answer I suppose it’s fine
So using this very simple model which sort of assumes the most ideal scenario with the initial average grow rate at 2% and starting population at 500, then it would take around 384 years
Thanks! I'm a fiction writer so math isn't my strong suit. I appreciate the help.
if you really thought about it the population from innitially grow linerly for the first 18 or so years
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Guys, how to do this? Pls help, thankss
is this for an exam
It looks like a past paper
ya ok
Yes, but it’s not that helpful
you need to figure out which number x can possibly be
You’re better off making it as a quadratic in sqrt(x) or isolating sqrt(x) and squaring both sides
Yes im studying for my exam tomorrow
ok cool
substitute x for t^k where k is an appropriate number
such that you end up with a polynomial
here clearly k = 2
then you get t² - 4t + 1 = 0 which you can solve
(Note that’s the same thing as making it a quadratic in sqrt x)
yeah
How to get 2 tho
you want all powers to be integers
you have t^k - 4t^(k/2) + 1 when substituting
the smallest k such that k/2 is integer is k = 2
if you have x^(1/3) + x^(1/2) + 1 = 0 for instance, you would choose k = 6, and so on
ok @mortal heart ?
it's the same as substituting x^(1/2) = t as @mint crescent suggested
Hmmm do we get 6 from the 5/6 and 2 from the 1/2?
lcm(2,3)=6
Ohh yes
6 is the smallest number such that both k/3 and k/2 are integers
Ohhhhh
indeed the least common multiple of 2 and 3
Okokk
Im gonna try
Guys is that an AS level or A2 question
I felt like i know nothing
I don't know what that is
but with practice you will remember things
and just trying things out
rewriting x - 4x^(1/2) + 1 as (x^(1/2))² - 4(x^(1/2)) + 1 is a very common trick
or rewriting sin(2x)/x as 2sin(2x)/(2x), and so on
always the same technique
my teacher called that the street sweeper technique for some unknown reason
add what you want to make it an expression you know how to deal with, and then subtract/divide/whatever what you added to keep the expression the same as before
here we rewrite x as (x^(1/2))^2
we want x^(1/2) to appear so that we get a polynomial in the variable x^(1/2), but to keep the expression equal to itself we square it too
thank you so much
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guys
about this
do i multiply the whole equation by 2?
ohhhh
$$t = 2\pm\sqrt{3}$$
suut
okkk
so $x = 5 \pm 4\sqrt{3}$
suut
btw are we allowed to set k whatever number we want for every question?
yes
if it’s a multiple of 2
it will always give you the same result in the end
but whatever you do you will end back with having to solve the k = 2 case anyway
so take k = 2
ummm
only quadratics are easy to solve
cubics and quartics can be solved too
but above that you have to use tricks to reduce to a lower degree
so we want k as small as possible
and hope to end up with a quadratic, maybe a cubic if you’re in university
ooohh
after this, i should substitute tbis to t and find k right?
you want to find x
we already know what k is, it’s 2
and we just found what t is
so you just compute x = t^2
as I did here
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i rly need help with the third inequality
ik im suppose to use the cauchy-schwarz inequality but idk how it works here
the first vector is x
the second vector is (sgn(x1), …, sgn(xd))
sgn is the sign function
in C-S
in R
right ok but where do u get the sign function from???
$||x||_2 = \sqrt{(|x_1|)^2 + \dots + (|x_d|)^2}$, right?
yeh
oh
wdym C?
the vector space is C^d not R^d
higher!
is this better?
yes
higher!
I do not remember my norms well ngl 
yeah but not all that helpful I think
yes
i mean these r my lecture notes so i think so
but it’s not extremely useful so far
you need to indeed use C-S
you understand my proof for R?
sorry what is C-S???
Cauchy-Schwartz
for instance if x = (2, -3, 5) then the second vector in C-S is (1, -1, 1)