#help-0
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Question b is what I'm trying to do.
I've been able to deduce that whenever two variables(e.g y and z = 0, then x will equal -2 and 2)
And I've marked all those points on a graph
a hollow sphere
how u might ask? well in 3 dimensions the equation for a sphere is x^2+y^2+z^2 = r^2
yh
if x^2+y^2+z^2>4 it means x^2+y^2+z^2>2^2
which means u have to remove a sphere of radius 2 units on the graph
mm not so sure about that
oh
equation of a sphere is (x-a)^ +(y-b)^2 + (z-c)^2
so since theres no number after the x y and z
i was thinking it would be a centre of 0,0,0
oh right
I’d think it’s centred at the origin
yeah that does make sense
and how do we know its hollow in this case
now z <= 100 so z^2 =< 10000
Cos of the strict inequality
u mean z<100 right
No the sphere
its not visible..
It’s hollow cos everything inside the sphere doesn’t satisfy the first inequality
the 4 part?
Actually that has nothing to do with strictness of inequality
but we need to also make sure that its not the entire 3dimensional whatever right
Wat
we need an upper bound as well
what plane?
Yeah I wasn’t talking about the 100 yet
its either referring to inside the sphere or the surface and the entire space outside the sphere right?
its always a sphere with a sphere of r=2 at the centre removed
we dont rlly care about size anyways
Everything inside the sphere doesnt satisfy the inequality
ahh ur right
ive just used the centre of the sphere to test that out
i can use 0,0,0 to substitute into x y and z right?
cos 0 ^2+ 0 ^2+ 0^2 is not greater than 4
what about the surface🤔
less go i was right 🙂
(this is i think the 1st time i have done a problem related to 3 dimensions)
what point could i use for that
wont be included
ig
z is the x axis perpendicular upwards to x and y right (in some places its switched, like blender)
it would only be included if it was less than or equal to?
yes
np
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1shero1
So you go from x=0 to x=r
Now instead of x you have rsin θ
So you’ve got rsin θ = 0 to rsin θ = r
That’s the 2nd one
In here
Yeah rsin θ = r
That’s x = r
Then you go oh sin θ = 1
θ = …?
So your new bounds are to integrate from 0 to pi/2
Look at this
x = r
x = r sin θ
r sin θ = r
sin θ = 1
Yep
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well i actually wanted to post the 8th question
but i dont get how to write and make calculations with the 2^- 's either maybe the logic behind them is the same as the question below?
can u translate the question?
"what is the result of the following calculation"
ah i see
let the fraction to be found = x
i am not gonna tex it, cus idk how
does the ... mean 2/2/2/2... infinitely
but then wouldnt thay give me some 1's?
wdym by 1s?
but i should know how many there are to add them?
literally 1
yeah see thats the trick
isnt that gonna be 2/2 so thats one "1"
its not 2/2
then again above that suppose another 2/2
its not 2/2
notice how the pattern is formed
does it mean we dont know the number on the dots?
yes
yes we dont know
but it still converges
.
eh..hold up lemme write it out
or does it like go as the others
go
2/2 but with a +2 in front
then again 2/2 ...
ok lets just for a minute
(rewriting the .../2 thats already written
think that there is a finite number of ...
hm
say 5
so we would have:
$$2+\frac{2+\frac{2+\frac{2+\frac{2+\frac{2}{2}}{2}}{2}}{2}}{2}$$
itzkraken.
yeah okay
but how do i calculate this
before doing that, if we had ... = infinity instead of 5
this would go on forever
so if u let this = x
can u write this interms of x?
@south crystal Has your question been resolved?
ajax4074
like this?
@south crystal Has your question been resolved?
Its 4
hm its not right
yeah how is that?
(i said this to myself)
The fraction part can be looked as
2/2+the infinite part/4
And the nxt term will be
2/4+the infinite part/8
And this thing will be equal to
2+1+1/2+1/4+1/8+1/16+1/32....
Wich is equal to 4
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Just cross checking this. Thanks
Please don't occupy multiple help channels.
You can ask this in your other help channel if you’re not working on the original problem
oh im sorry i didnt know that
how do i like end that chat?
im not sure how this works sorry
you mean close this channel, or end the conversation in your first one?
end the convo in the first one, coz i got tht..thank you for that
how about you end this one and go back to the other chat? you can ask multiple questions in one help channel
okok
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can someone explain to me how they got this sketch
I understand these other two
but not this
can you guys teach me how to get that graph
is it just y = -x
@true sandal Has your question been resolved?
nope
@true sandal Has your question been resolved?
it's y ≥ -x, which is all of the stuff above the red line y=-x
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Hey! How do we find the value of p which gives us the maximum area of a rectangle under the curves g(x)= e^x and h(x) = e^-2(x-p)
Any progress so far?
@tidal stream Has your question been resolved?
Let's assume that the point A has coordinates (x, 0)
Then the length of AD would be e^x, right?
yeah
Note that BC has to have the same length
Okay wait before that let's introduce a variable denoting the length of AB
Let us call it a, doesn't matter
mhm
Then B has coordinates (x + a, 0)
Meaning the length of BC, using a similar argument, should be e^-2(x + a - p)
But, like already mentioned, we should have AD = BC, so here comes our first equation: e^x = e^-2(x + a- p)
Before moving on, we can simplify that
Taking ln of both sides yields x = -2x - 2a + 2p and x = 2(p - a)/3
So now let's find out what would the area be in terms of our variables
S = AD * AB = a * e^x
Okay maybe it could have been better to write a in terms of x, that yields a = p - 3x/2
Meaning S = (p - 3x/2)e^x
Btw there is no more information given I assume, is that right?
and now diff and make =0 and sub back into s
yeah
Could you show how the problem is originally stated?
Umm we had our test this morning and i couldn't do it and was thinking about it....we havent gotten our papers back!
but yeah they gave us the 2 functions and a similar diagaram and asked us to find the value of p which gives us the max are of the rectangel
Okay, I guess we need to assume p is some fixed number and solve for it only after we get the expression for S in terms of p
So it's actually finding the maximum of the maximum area
The derivative of S with respect to x becomes -3/2 * e^x + (p - 3x/2)e^x
We set it equal to 0 and divide both sides by e^x since it can't be zero
We get -3/2 + p - 3x/2 = 0 and solving for x yields x = 2p/3 - 1
And yes, like you said, we now plug in back into S
the value u get once u sub it back
Yeah that's correct
Which is like really weird as that expression doesn't have a bound
mhm
can we sqrt that and make it equal to a side?
coz it needs to be a square right?
Are you sure it wasn't something like "so that the maximum area of such rectangle is minimal"?
We aren't dealing with a square though
yeah but isnt it assumed that the max area of a rectangle only occurs if its a square right?
Alright, let's check if what we got is a square
The width was a, which turned out to be p - 3x/2
Oh, which simplifies to 3/2 actually
Interesting, the width of the largest rectangle always has to be 3/2 regardless of p
And the height was e^x, which isn't a constant (it's dependent on p in the maximal rectangle case)
So, no, what we are working with is a rectangle
hmm okay...
yeah im sure
@echo socket
Either way the question doesn't seem to make sense, I would like to take a look at how it's stated
yeah....
im pretty sure thats what the question said tho....
@echo socket
Anyway...youve been great help!
Is it okay if i dm you more doubts and stuff?
Sure
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Hi
it should be +- 3
Subtract
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No that isn’t it
(x+4)^2+9=0 is not the same as (x+4)^2=9
It’s (x+4)^2=-9
@strange fractal
No real x intercepts
Ohhh ok thank u
yeah mb!
Wait wdym by real
dww
You’ll learn later
you can get non real sols
Are u serious am i gonna be learning about fake numbers soon
NOOOOOOOOOOOOOOOOOOOOIIIOOOOO
haha!
Just make sure then the eqn of the quadratic is in vertex form you realise where ther vertex is and the shape of the graph
then u'll easily catch it when u dont have x intercepts!
Thanks 🙏🙏🙏
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how to read the RHS after the equals sign? i understand the integrand from negative infinity up to y. f(x) is the probability density function. what is meant by dx
derivative of x
can you help me to understand what is meant when there is both a derivative and the integrand symbol in one equation
is it meaning like the integrand of f(x) in that space times the derivative of x?
@alpine sable Has your question been resolved?
easy answer : it's just part of the notation of the integral : \int f(x) dx means integrating f with respect to the variable x (i.e. x is the variable of integration)
hard answer https://en.wikipedia.org/wiki/Differential_form
In mathematics, differential forms provide a unified approach to define integrands over curves, surfaces, solids, and higher-dimensional manifolds. The modern notion of differential forms was pioneered by Élie Cartan. It has many applications, especially in geometry, topology and physics.
For instance, the expression f(x) dx is an example of a...
@alpine sable
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hi :)
i need help with this problem, specifically 2.3
i got 720 degrees for 2.1, and for 2.2: p = 1/2; q = 30 deg
i dont know where to start with 2.3 :(
channel busy please move
h(x)/k(x) ≤ 0 precisely when one of the following holds:
- h(x) and k(x) are both positive;
- h(x) and k(x) are both negative;
- h(x) is 0, but k(x) isn't.
is my understanding correct that it will be for all the values green except for those 2 points then?
fuck ok sorry hold on
i accideally misread my own ≤ as ≥
for ≤ you want either h and k to be of opposite signs, or h(x)=0 and k(x)≠0
some of the green bits you highlighted don't work for that, such as just to the left of -180
oh i see okay
should i just exclude that whole section between the 2 x intercepts
the first pink area up to -180
@cyan grove Has your question been resolved?
@cyan grove Has your question been resolved?
@cyan grove Has your question been resolved?
@cyan grove Has your question been resolved?
Yes
Can you figure out which endpoint you're supposed to include and which one you aren't
@cyan grove Has your question been resolved?
ah
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hey guys what does this statement exactly mean
"Give the expressions of the joint probability distributions fX1,X2(x,y) and FX1,X2 (x, y) in terms of γ1 and γ2 and θ. Deduce the cumulative distribution function of S, FS(s)."
where y1 (gamma) and y2 (gamma) are parameters of X1 and X2 and theta is the parameter of copulas
like clayton or frank copula has Cx
S is X1+X2
Cθ(x,y)=xy+θxy(1−x)(1−y), θ∈[−1,1]andx,y∈[0,1]
@teal plaza Has your question been resolved?
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I dont see what I'm doing wrong in my work?
@obtuse folio Has your question been resolved?
I literally followed this example^ :((((
I dont know what I'm doing wrong
ok whatever idk anymore
im gonna sleep
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How do you determine whether this is no n linear or not
Can you recall the definition of linearity?
That if you graph it it will look like a line and will go up by a set amount?
f is linear iff additivity and homogeneity are satisfied, that is:
f(x + y) = f(x) + f(y)
f(ax) = af(x)
Ah ok
Can you check whether f(x) = 9x/5 + 32 satisfies any of these two?
@daring rapids Has your question been resolved?
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Lin Alg Question:
can someone explain how c is false and d is true?
I originally had C as true and here is the explanation i had:
Since tx is in U, then scalar multiples of tx are also in u. For values of t not equal to 0, we can multiply by 1/t to get x alone, and for t equal to 0, we get the zero vector which is part of the subspace by definition
okay, you remembered that 0 is a real number but I don't think you really thought about what you were saying
i think you proved the converse, that if x is in U then tx is in U
which is true
For d , linear combinations also belong to that space
wouldnt that just give 0 vector?
Yeah, and it's clear that 0 is in any subspace
use my substitutions and read the statement
tell me what it translates to
So when t = 0, the statement becomes "If 0 is in U, then x is in U"
Which is false assuming U is not V (can't remember whether subspaces are supposed to be proper or improper subsets)
the “for all” could be confusing
improper, but ofc it doesn't matter here
subspaces not necessarily proper
Alright
if 0 is in U then x is in U
oh, wait
but what if its just a random x value
cuz 0 is always in the set
!!
ayyyyy
which topic is this related to and what grade?
that’s why i chose x such that x is not in U for a counterexample
this is linear algebra 2 in my university
thanks thanks
for d, would i use the additive inverse to prove it?
im not 100% sure how that would work
for d, see this
consider the sum and difference of the given elements in U
(x+y)+(x-y) = 2x
therefore x is in U
am i on the right track there?
and if x is in U then -x is in U
(x+y) + (-x)
does that work?
to prove y is in U
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can anyone here help me out with copulas and how to find joint cdf of 2 continous random variable?
Cdf is continous distributive function?
cumulative
@teal plaza Has your question been resolved?
@teal plaza Has your question been resolved?
try an advanced channel and a more specific question
i did put : (
what problem
i have a copula dependence function
send it
for 2 exponential random variabe
i want t find the joint cdf
both exponential variables are not independent
i have written in #advanced-probability
lmao
are you?
I saw it
which grade are you in?
I have not graduated
youre still in school?
Yes
no hate or rudeness. But sadly this is post grad level stats
so you might not be able to help me
but thanks for your time
latexing your question would also help in that channel
but yeah, the activity is not as high
and ur just gonna have to wait for someone who knows. . .
what does latexing mean?
@teal plaza Has your question been resolved?
@teal plaza Has your question been resolved?
writing in latex. @ocean seal
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I'm trying to solve $$\cos{(x)}\frac{dy}{dx}+\sin{(x)}y=1$$ I don't see what is going wrong. I rewrite as $$\frac{dy}{dx}+\tan{(x)}y=\sec{(x)}$$ and then choose my integrating factor to be $$u=e^{\int{\tan{(x)}}}=\ln{(|\sec{(x)}|)}$$ But then when I multiply this factor back through I get $$\frac{dy}{dx}\ln{(|\sec{(x)}|)}+\tan{(x)}\ln{(|\sec{(x)}|)}y=\sec{(x)}\ln{(|\sec{(x)}|)}$$ Which then I should be able to rewrite the left hand side as $$(\ln{(|\sec{(x)}|)}y)'$$ but it doesn't shake out when I differentiate that, it is missing a term and not equal to he left hand side. Could anyone point out what I am missing?
austinu
integral of tan(x) is ln(|sec(x)|)
you forgot the exponential for the integrating factor
@vapid shuttle
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Not sure how to solve these questions... the hint at the back for Q15 suggests to use the fact that 5^2 is congruent to 2^3 (mod 17)
but idk what to do after
toby____
hint: $5^{2m+1} = 5\cdot (5^2)^m$
toby____
@brave dagger Has your question been resolved?
hey Toby thanks a lot for the hint
I tried it out, but I'm still stuck : ((((
so here's what im getting
$5^{2m+1}-2^{3m+1} \cong 3 \cdot 2^{3m} (mod 17)$
statisticalcat
Nope, I tried doing that rn
im getting everything but the thing to be proved
if $17|(3 \cdot 5^{2m+1} + 2^{3m+1})$ then the $2^{3m+1}$ factor next to (mod 17) must be negative....
statisticalcat
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just look at the first two equations
(did you already post this a few weeks ago? I remember seeing it)
i just checked
i didnt
this is the first time of me asking this question
also yeah
wow
it looked so complicated i didnt see that the first two equations being the same giving different answers
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How would I get an equation for this?
@alpine sable Has your question been resolved?
<@&286206848099549185>
soo you just gotta think of a function that is defined for x>3 and has limf(x)=-inf
right?
Yea
do you know what Graph A is saying?
or is asking you to draw
as X gets bigger Y gets smaller
what function could do that?
@alpine sable Has your question been resolved?
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how do I know the equation based on the table of values that it provides
or whatever you call this sort of chart
i mean it'll be guessing regardless
you can’t guess
there’s an infinite number of functions to guess from
so you can’t know the exact function
there's no way to know for sure
the exercise here is to come up with a "simple" function that matches these points
i mean you can guess
so yes, built out of multiplication, addition, exponentiation, maybe some squares or square roots, etc
since x is going up by 1 each time, it may be helpful to examine what happens to the output on each line, compared to the previous output
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This is a graph of f'
i need to find x values the inflection point(s)
i thought it was 10 but i was wrong and this graph is kinda wonky its confusing me
hmmm handmaded graph, this is too difficult for me lol
i didnt!!!
anyone help with a-level math?
its just like this lol
Please read #❓how-to-get-help
bruh
its hella small too i had to zoom in
send a screenshot of the original question
that's the graph for f', not f
yeah
do you know what an inflection point is?
when is f’’ = 0?
4,10,14?
why 10?
bc it looks slightly cubic and the slope appears to be 0
idk
it looks like its where the concavity changes
wait nvm no its not bc f' is decreasing from (4,14) which means f'' is concave down that whole time so its not actually changing
its only changing at 4 & 14
but thats kinda throwing me off it looks cubic? does that mean anything
@coral thorn
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How do you factor integers in quardratic fields such as Q(√-2)? I know that, in the case of Q(√-2), every integer has a unique factorization but how do you acutally work this out? Does Q(√-2) and Q simply have the same primes because the primes in Q can't be further factorised in Q(√-2)?
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Do we know of any set of numbers which are 'sparser' than the primes (I suppose I mean the percentage of numbers in the set under n grows slower than the primes at the limit, sorry for the math gibberish) where some two of the numbers can add to make any positive even number?
@grand karma Has your question been resolved?
Non-even primes?
thats a bit of an unclear question hahah but i guess you could take the set of prime pairs
or twin primes
that is, primes that only differ by 2
for example 11 and 13
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determine convergence/divergence, evaluate if it converges.
so i used l'hospital's here, but how would i find this limit by hand?
intuition tells me this converges to 0, but im trying to prove it.
if it's real analysis, you'll have to take a bit more care
this is just calc
so just use what i said above
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I got lost at integrating, which is at the bottom. Did i write my integral correctly in the first place?
dont upload random files
you didnt plug in your bounds correctly
I tried both ways so i think thas why its switched in the photo but either way I got confused at that point. Whichever term you decide to subtract, I didn't undersand what to do with the x's i guess
or how to simplify that expression
upper bound minus lower bound
what do you get if you plug y=x^2 into the antiderivative
and what for y=sqrt x?
I should have asked in the other order cause sqrtx is the upper bound
so after you switch around, yes
okay, ive switched them but im still confused on the simplifying to then integrate 1 and 0. Here is my revised expression
you plugged the bounds in. why are they still there
now its just a bit of power rule
@raven dirge Has your question been resolved?
this looks really wrong
@raven dirge Has your question been resolved?
I integrated wrong at x^2/2, it should be x^3/3 but otherwise I still don't know how to do the rest of this problem
I went on symbolab and it said 3/4, but I didn't understand the solution
is anyone able to help :(
@raven dirge your setup looks fine, I didn't follow the integration along carefully, but it's polynomial so I don't doubt you did it correctly. However, I do have one tip!
Because you have symmetry about the line y=x you can do the integral from x^2 to x instead of x^2 to sqrt(x) and double the result. This should make your integral simpler to compute
It also gives you a way of verifying your work
\begin{align*}
\int 3x \sqrt{x} \dd{x} &= 3 \int x^{3/2} \dd{x} \
&= 3 \cdot (2/5) x^{5/2} + C \
&= (6/5) x^{5/2} + C
\end{align*}
omnipotententity
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Hello so I didn’t have enough time for my test so I randomly picked the last answer
Give me one second
The question was
Was this right
I think it was wrong
It shoulda been the last one
.close
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i have a physics problem
but im not sure if this is where to post but heres the problem
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for these 2
@raw nacelle Has your question been resolved?
well not necessarily my work, just my answers
Well show your work
That works
or a picture
I used to take pictures on my phone and email them to myself to get them on my pc to send here
now I just upload them from phone discord, or type my work
lol i'll just type em out, thanks for the recommendation tho
-.1 < | x^2 - 16 | < .1
austinu
close
zoumaldo.
that gave me the decimal, which is in my answer up there
and then I took the absolute value of the difference for my 2nd answer
first picture btw
zoumaldo.
solved to get
zoumaldo.
was wondering if this was sufficient?
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hey guys
you know how when you differenciate cos, it becomes -sin
✅
is there such thing as differenciating -cos
well if you differentiate -cos it becomes sin
and does it result in sin
Yes, it becomes sin
Yup
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✅
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i need help on all these questions
- not sure where to begin
- also not sure where to begin
- I know how to do polynomial division and i have attempted this problem, but im confused on how to do this problem when you have a gap in two exponents
do you know that you can uniquely define a quadratic with 3 distinct points?
no?
how many variables does y = ax^2 + bx + c have?
2
ok, so a, b, and c
if we changed them we wouldn't have a quadratic anymore
right
so a quadratic is defined by what a, b and c are
yup
so we need 3 "pieces of information"
and these three pieces of information are given in the question
suppose we are told 3 distinct points
$(x_1, y_1), (x_2, y_2), (x_3, y_3)$
frosst
and we are told these 3 points lie on the quadratic
yup
then we can construct such a system
$y_1 = ax_1^2+bx_1+c\
y_2 = ax_2^2+bx_2+c\
y_3 = ax_3^2+bx_3+c$
frosst
so, by making this system, we could combine all three of these to make the quadratic equation
yes
The second option would be to use Lagrage Interpolation
but actually we are going to do something different to this
because if we look at our points
they are special!
they are not just any 3 points on the quadratic
what do you notice about the 3 points given?
this was just to show you that a quadratic is uniquely defined by 3 distinct points
the x intercept
they are the x intercepts!!
ok
we know another form of the quadratic besides this
$y = a(x-b)(x-c)$
frosst
where b and c are the roots of the equation
vertex form?
not quite
ok
we know from the points that -5 and 2 are roots right?
yup
(also note these a, b, c's are not the same ones as the one before)
frosst
and now we plug in the third point
so this is the fundamental concept for that question
ok
a few ways to find the a b c's but they all use the fact we need 3 pieces of information
ok
,w solve for a, -1 = a(4+5)(4-2)
looks good
yup, a cubic is a parent function of y=x^3
ok
use the previous formula
(also notice that a quadratic needs 3 pieces of information, a cubic needs 4 pieces of information)
ok
this means we will get a family of cubics that satisfy the given condition
because the conditions dont constrain us enough to have only 1 solution
ok
which formula
y=a(x-h)(x-k)
do you think you could extend this to cubics?
yes
what would it look like?
by putting another x-
show me
ok now make this cubic have roots 2, √7 and -√7
what does it look like now
y=a(x-2)(x+sqrt(7))(x-sqrt(7))
and let's see what you've done for Q5
ok
i would write (in an exam) $a\in\mathbb{R}\setminus{0}$
frosst
for Q5, I know how to do polynomial division but I dont know how. to do it when you have a gap in exponents
,rotate
im sorry its slanted
frosst
i wasnt really sure what to do with that -x^2 and 2x^3
try putting in 0x^3 between x^4 and x^2
ok
give me a minute or so to do it
does 0x^3 + 2x^3 = 2x^3?
nvm
@median oar ok i think i got it
i got 2x^3+2x^2+x+4. remainder is 9
Then there you go
find one solution
x^3+5x^2-2x-24=0
there is an "obvious" solution
when you are given something like this start with checking 0->1->-1->2->-2
ok
so you should plug in numbers for x
?
yes
ok
if the number you plug in results to 0 then that number is a solution
sure but it shouldnt be too hard to do it with you head
obviously 0 doesnt work for example
yeah
1 doesnt work
-1 also wouldnt work
bingo
2 works
so x=2
x=2 is the solution?
ok
when a polynomial has a solution x=r
then it can ALWAYS be written as (x-r)(something)
ok
so how do you proceed?
not sure
your saying (x-2)(something)
?
yes in this case x=2 is a solution
ok
we got x^3+5x^2-2x-24=0 so (x-2)(something)=0
funny thing is i dont remember how the division works...i ve always just done it by myself
ok i got it
whats the something?
ya i get that feeling
x^2+7x+12
i can show you if you want
correct
so now that i have that whats next
so what s this things solutions?
dont know
well it s just ax^2+bx+c
lmao no
oh
to find the solutions of this you gotta find the discriminant
whats discriminant?
isnt b^2 - 4ac the discriminant and not the whole formula?
yeah but students normally find the discrim first then use it for the whole thing
oh thats interesting to know ! 👍
bing you ve seen this before right?
i mean you ve been taught how to solve ax^2+bx+c=0
yes
well then you can solve x^2+7x+12=0
with this
using quadratic equation?
ok
ok
i got x = -7 + or - sqrt(1) divided by 2
well i could simplify the sqrt
well somthing tells me that if you plug in -7 or -1/2 none of them will work
ok
do it again or show your work if you cant work it out
yeah this is correct...so the solutions are?
bruh
it is
oh
do the +sign first
ok
the solutions are (-7+1)/2 and (-7-1)/2
it s -3.5+-1/2
ya
wait i did
nice
so is it correct?
yeah
so what are the solutions of x^3+5x^2-2x-24=0
the real solutions are -4, -3, and 2
those are also all the solutions
ok
alright
ill figure out the last question on my own or ill come back
