#help-42
1 messages · Page 114 of 1
this is the interval
pi/8 and 7pi/8
so n wouldnt work here in this scenario
correct?
yeah I know
just wanted to clarify
I was trying to get you to arrive at the general solution and then find all n s.t. it's in the interval
okay
so that would mean
besides pi/2
umm
wait is that it
is it just pi/2
no other values?
yeah
only $n=1$ makes $\frac{n \pi}{2}$ lie in $\left[\frac{\pi}{8}, \frac{7\pi}{8} \right]$
Civil Service Pigeon
thank you so much
i will definitely ping you in the future youre the best tutor i had
LOL
have a good night!
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oh uh
about that
Please do not ping individual helpers unprompted.
oh oops
we had to make this lol
gotcha
on this note, don't send ppl message requests out of the blue either
i wont dont worry

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let $xy=z^2$ prove that there is always $p,q,r$ where $\gcd(q,r)=1$ and
$$x=pq^2$$
$$y=pr^2$$
$$z=pqr$$
Skissue ping4response
this question is wierd im not sure what path i go for
note p,q,r,x,y,z are natural numbers
@tall moon Has your question been resolved?
Okay maybe I'm being dumb but I don't think this is true. Isn't this a counterexample?
(x,y,z) = (8,18,12)
8*18 = 12^2
If x = pq^2 = 8, and gcd(p,q)=1, then the only possibility is p=8, q=1.
But if p=8 and y = pr^2 = 18, then r is not a natural number.
@tall moon
p=2 q=2 r=3?
but gcd(p,q)=1
oh, that seems more plausible lol
let $xy=z^2$ prove that there is always $p,q,r$ where $\gcd(q,r)=1$ and
$$x=pq^2$$
$$y=pr^2$$
$$z=pqr$$
Skissue ping4response
streak of me fucking up the question
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v_c has higher speed right?
hi
hiii
hiiiii
yes
thing is
idk
cuz
im getting a 50% response ofr both
someone said
since its elastic they share KE
we're not given whether it's elastic, but all we need for the problem is conservation of momentum anyway
so v_c isa faster?
it must be
you can write v_A and v_C in terms of the initial speed of the ball B, the masses, and the final speed of the ball B to demonstrate that
okay my logic was that if i do a system of like conservation pf=pi
since the b ball goes back
the velocity of the ball becomes negative for final therefore the box must have higher velocity
yes. you can express that mathematically by expressing the initial and final momentum of the system in terms of the variables mentioned above
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why does it give 1 even though i specified the bounds
4-4 = 0 so that lies outside of 1-3 or -1--3
ty
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How do i determine which is bigger wothout the calculator?
e^pi and pi^e
Generally the one with the larger exponent is greater
No
The maxima of the function x^(1/x) occurs at x = e.
So e^(1/e) > π^(1/π)
Hint: After this, you may just do some algebraic manipulation to this inequality.
so 2^3 bigger than 3^2
My bad ,not always true i guess
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Prove that:
[UA1V] + [A1ZW] = [UA1Z] + [WA1V] = 1/2 [UVWZ]
Given that UVWZ is a rectangle.
area of triangle = 1/2 * base * height?
I mean, use that here...
@remote mural Has your question been resolved?
Z26W26 = B27A27
For triangle V26P26Q26, area = 1/2 * V26W26 * P26Q26
For triangle S26V26R26, area = Z26V26 * 1/2 * S26R26
Right? And now the sum = 1/2 (Z26W26)(P26Q26 + S26R26) = 1/2 (B27A27) (S26P26 + R26Q26) right?
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Ok bro
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How do I calculate how many arrangements of n objects are there, if k of them need not to be used
Take e.g. a, b, c, d, e, f and say e and f dont need to be used
so valid arrangements are e.g.:
abcd
abedcf
efabcd
eabcd
bfadc
I need something efficient
currently the only way I have is summing up some stuff
nvm, i optimized something else instead so i might not need this
yep
I was calculating all binomial coefficients (n choose i) with 0 < n < some bound and 0 < i < another bound instead of just using pascals triangle. Silly me
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x * sqrt(25 - x^2)
to maximize this geometrically we are maximizing the inscribed rectangle in a circle?
is that true?
well idk in my mind it kinda makes sense but can someone explain regardless
Yeah, that's right. You can draw the picture to see it
how?
well that part i get
i mean sqrt(25 - x^2) is a circle with radius 5
well only the positive branch
Maximizing a function and twice the function is the same anyway
and where does the rectangle come into play here
no i'm asking how maximizing x * sqrt(25 - x^2) translates to maximizing the rea of a rectangle in a circle
what's the reasoning for that
i kinda know that it is the case
but i can't justify it
or explain it
Draw the circle. Draw the rectangle. Label the lengths of the rectangle
If you write the expression for the area, it's the same function
the diagonal is 10?
let x be the width and y be the length then x^2 + y^2 = 25
Not 100
i mean 25
This
wait what
the diameter is 10 though?
so we have a right triangle with hypotenuse of 10

no?
Okay, there are several ways to draw this.
Right triangle with hypotenuse of 10 is fine
No, because that has diameter 20
Radius and diameter are different
i'm talking about the triangle though
😭
just the triangle alone
it's just pythag
Draw it on coordinate axes
That's not your x and y
uhhh i just gave it some labels
Draw this equation, but not those labels
like coordinate geometry free
Until this picture, I had no idea why you were talking about hypotenuses or triangles. You really don't want either in this question.
yeah i was confused too
i think u were talking about a circle
and i was talking about pythag lol
Now you can find the area of that
Don't use the diagonal
Label the positive x-intercept x
Then find the y-intercept in terms of x
Then find base and height
Okay, after further review, this will work, but it takes some algebraic cleverness to see why.
Yeah, or you can just use the equation of the circle
This here
sure if radius is one diagonal of a rectangle
Maximizing a function is the same as maximizing four times that function
then there's 4 such rectangles
sure makes sense
how would i do it via this
h^2 + b^2 = 100
100 - b^2 = h^2 -> h = sqrt(100 - b^2)
area of rectangle is b * sqrt(100 - b^2)
hmm i need a scaling factor and maybe some factorization
okay
yeah that should work
2k * sqrt(100 - 4k^2)
2k * sqrt(4) * sqrt(25 - k^2) = 4k * sqrt(25 - k^2)
alright thanks for the help!

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i just need help here
would my c stay as square root of 217
or do i make it 14.73
i know it cant be simplified further
both are correct, i was always taught to keep a square root but it is your choice
would i do it like this: (7+√217, -10) or (7+14.73, -10)
oh okay
so when i calculate it
its same answers right
okay was just confused
but very very similar
this is what i got with 14.73
okay thank you
keep it as sqrt, as further calculating after approximating won't give you the correct result (if you have to use the 'c' after calculating it). Supposing it's a theoretical math class.
thank you so mch
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!status
What step are you on?
1. I don't know where to begin.
2. I have begun but got stuck midway.
3. I got an answer but I was told that it's wrong.
4. I got an answer and would like my work checked.
5. I have a question about someone else's work/solution.
6. I have completed the problem and don't need help anymore. Thank you.
7. None of the above
it is zero right?
the multiplicative inverse of the radius is 0
the computer homework program is marking 0 wrong
how is it infinity
Just to help you for next times
instead of computing $\frac 1R = \lim_{n\to \infty} \left |\frac{a_{n+1}}{a_n} \right |$
rafilou is not not born in 2003
directly compute $R = \lim_{n\to \infty} \left |\frac{a_{n}}{a_{n+1}} \right |$
rafilou is not not born in 2003
if you wanna use the ratio test
this is easier
then you won't forget to input 1/(what you got) with this method
how is 1/0 infinity
if were not taking the limit of r
its infinity when you take the limit of 1/infinity
?
if you don't like 1/0
think of 0 as limit of 1/n as n-> infinity
then 1/(1/n) = n
so when n-> infinity
goes to infinity
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$\lim_{x\to+\infty} \frac{x+1}{\sqrt{x^2+x}-\sqrt{x^2+1}}\cdot\ln(\frac{x+2}{x+3})$
you don't need a \ before your +
$\lim_{x\to+\infty} \frac{x+1}{\sqrt{x^2+x}-\sqrt{x^2+1}}\cdot\ln(\frac{x+2}{x+3})$
Can someone help me
Have you given this a crack yet?
What

What f mean
You have to show your work. “For you it is inf” but in reality is not
,w lim_{x\to+\infty} \frac{x+1}{\sqrt{x^2+x}-\sqrt{x^2+1}}\cdot\ln(\frac{x+2}{x+3})
What
It's very heavy

Heavy blow
Mmm
Lemme think
But if x goes to infinity how does it come out as a negative number
the stuff in the log is negative
If the functions are positive
They aren't
The logarithm is defined for x>0 so it is positive
Like √x
It has no negative values
,w log(1/2)
Oh
But here we are talking about limits
The limit of the log is in positive numbers
The limit of log(x) as x approaches infinity is infinity
That's not what you have though
Why
,w graph ln((x+2)/(x+3))
Replace
(x+2) in the numerator
With (x+3 -1)
And split in 2 fractions
(x+3)/(x+3) -1/(x+3)
You have 1-1/(x+3)
$\ln(1-\frac{1}{x+3})$
Wobble
This is between 0 and 1
Its 0
0^-
That is why the limit is negative
Wobble
What's "it"

This
Output , bro we are not on a PC
no and no
Why?
Because those words don't even make sense
what's the limit of -1/x
what's the limit of 2x * -1/x
No not by lhopital
You can't apply lhopitals to that
Oh okay
-2
But I have a fixed 0
.
What's a fixed zero
Wobble
Wdym
The limit is zero
In both cases
It's not "0+ε", it's not almost 0 or inexactly zero or 0^- or any of this other stuff which has no mathematical meaning which you keep making up
It's just zero
What
Ok nothing you say ever makes any mathematical sense
Here's an example that the limit indeterminate form 1^infinity does not approach 1.
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Here it seems my notation is used
Why can't I do anything😭
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confused where to start for this
@radiant moss Has your question been resolved?
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Can someone please tell me what I did wrong??
Please don't occupy multiple help channels.
You messed up here
You went from 5 + x^3 on the left to 5x + 3
Somehow
yeahh I figured it out the 2dn time
thank you so much!!
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e right?
makes sense to me
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Kenzo
suppose x and y are nonnegative such that x + y = 20, then consider f(x,y) = x^2 + y^2 and maximize/minimize this using the given
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x+y = 20
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from this
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Kenzo
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x + y = 20
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now we need to maximize it first
we know since x and y are nonnegative that means x>=0 and y>=0
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because thats what im interested in
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because of this, this means when we subtract 2xy from 400 we are subtracting a positive number
so the larger the product is, the smaller x^2 + y^2 will be
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now for the minimum
well i guess we could do
$\frac{x^2+y^2}{2} \geq xy \implies x^2 + y^2 \geq 2xy$
syecko
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and if x^2 + y^2 = 400 - 2xy we have a minimum at equality so xy = 100 or x^2 + y^2 = 200
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AM-GM inequality
this is your minimum
are you supposed to use lagrange multipliers
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ik the answer i dont know how to solve it
left side is also (x^2 + 1)/x
if you subtract both sides by that you’ll have 0 = 0
which is true for all real numbers
0 is excluded cuz well it’s not in the domain of (x^2 + 1)/x
🤔
see this
$\frac{x^2+1}{x} = \frac{x^2+1}{x}$
knief
also well they’re identical everywhere except where they’re undefined
it’s just a true statement with the added condition that x ≠ 0
so that’s that too
oh okay got it
it’s 2, e, pi, sqrt(2), 10, -13748884 etc
well 0 is a real number, it’s just that we can’t divide by zero
and x is in the denominator here
so if x = 0 then it’s undefined
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using law of cosine must find x
what i have rn is (8)^2 = (a)^2 + (9)^2 - 2(9)(a) cos 60 but idk here to go from there
Use law of sines to find the missing angles
I guess you could even just use law of sines tbh
yea but the topic we're on is law of cos so idk if i can use law of sines
unless it was like you said where i can use cos after ? idk
But yeah I think your method works one sec
okk
yeye
Once you’ve expanded everything it s a quadratic equation in x
It’s a^2 -9a + 17 I think
yea i tried that too n im still getting a weird number
well
two numbers
maybe this isnt the correct method n i should jus do law of sines tbh
idk
im supposed to use law of cos tho
I mean it should work are you really expecting a nice result?
i mean kinda
my professor said we shouldnt be seeing really horrendous numbers
plus im getting two diff numbers
You’ll get different numbers but usually only one makes sense
In either case there could be multiple answers
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Kenzo
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well, why would you start with x^2 + y^2 = 20?
are those your two nonnegative numbers?
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did you make them squared so they were nonnegative
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well the sum of the squares would then be x^4 + y^4
why not just use x and y
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it doesn’t say "the sum of the squares of two nonnegative numbers is 20"
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yea but this isn’t two
but it doesn’t
it doesn’t say it’s 20
it says make it as large as possible
and as small as possible
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x + y = 20
then it says find the numbers x and y if x^2 + y^2 is a maximum
and then do the same for a minimum
the sum of the squares is just x^2 + y^2
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yes
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mhm
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this is what’s given
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ok great
now there are like 3 ways we can do this
but seeing as you’re taking single variable calc
i guess we’re supposed to just do differentiation
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this seems so easy with algebra but whatever
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so
let’s consider the expression x^2 + y^2
what do you want to call it
s?
for sum
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hmm yea why wouldn’t we just use algebra here?
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$x^2+y^2 = 400 - 2xy$
knief
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do they do this?
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what do they do
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wdym
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,rotate
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$\nabla f = \lambda \nabla g$
knief
but you don’t know this
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i think it would be fun to do it this way
but let’s do algebra
you get this right
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$(x+y)^2 = (20)^2$
knief
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lol would you rather not
i can show you all 3 ways
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because i want to know about the sum of the squares
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i’m concerned with x^2 + y^2
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ok the only downside of doing it this way is i don’t think you know inequalities
do you remember
$\frac{a+b}{2} \geq \sqrt{ab}$
knief
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ok then we can do it another way
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no this is just algebra
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alright
so
if x+y = 20, what is either of them in terms of the other
isolate x or y
doesn’t matter
this way is just boring imo
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but this is how you do optimization problems usually
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nah boring and longer imo
yep
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i mean it’s probably better for you because this technique is more relevant to future problems
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Kenzo
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it’s supposed to be + btw
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yea
multiply by -1
since -x
and power rule of course
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Kenzo
yep power rule, bring down the 2 multiply by -1
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inside stays the same thouyh
Kenzo
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knief
yea i forgot the 2
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2x - 40 + 2x
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use second derivative test
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you can
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f’’(10) = 4
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f’’(anything) = 4
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no matter the x input it’s still 4
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is 4 > 0?
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which means x = 10 is a ?
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the big thing about optimization is that we are given CONSTRAINT EQUATIONS
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yea
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yes like for instance x + y = 20 is considered a constraint
like it’s something that must be satisfied
but there’s a hidden second constraint equation
which will give us the maximum
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can you tell me what it might be
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no
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$x \geq 0 \quad y \geq 0$
knief
these are our added constraints
coupled with the fact that x+y = 20
all three must be satisfied
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so we look for i guess you could say critical points or boundary points whatever
which would be when x = 0 or y = 0
and going back to the algebra i said earlier
$x^2 + y^2 = 400-2xy$
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knief
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well it’s just the boundary of the interval
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so here we look at the boundary
and that yields x = 0 or y = 0
which means
x^2 + y^2 = 400
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which would be when x = 20 and y = 0 or x = 0 and y = 20
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so we still didn’t find the minimum
we only found where it occurred
at x = 10
if x = 10 what does y =
remember x + y = 20
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we could’ve done this much simpler imo but this way also works
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well because you’re learning calculus
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so you’re supposed to use calculus techniques
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fire
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yea i did today
but there isn’t that much for me to study
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mostly doing the last hws
in like half an hour
i have a quiz tomorrow
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fun
yo i’ll show you the other way
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or maybe even the calc 3 way
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id do the same for maximum btw
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$\frac{x^2+y^2}{2} \geq \sqrt{x^2y^2} \implies x^2 + y^2 \geq 2xy$
knief
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yes this is from^