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
#help-49
1 messages · Page 105 of 1
sure lol
$bc=ak_1$.
\
We now divide across by $c$
\
$b = \frac{ak_1}{c}$
A dense set
Have to figure out how gcd(a,b)=1 is relevant here
what is the proposition mentioned?
what does the proposition on page 152 say
oh perfect
so 1=ak+bl
here's the hint that makes everything fall together: multiply both sides by c
$1=ak+\frac{ak_1l}{c}$
A dense set
A dense set
Which proves $a \mid c$
A dense set
wish I had thought of this
bezouts would have never struck me
$ab=pk_1 \implies b= \frac{p}{a}k_1$
A dense set
wait
oops
I was accidentally proving a\mid p and b\mid p
We prove the contrapositive, if $p \nmid a$ and $ p \nmid b$ then $p \nmid ab$
A dense set
$a=pq_1+r_1; 0<r_1<p$
\
$b=pq_2+r_2;0<r_2<p$
\
It thus follows that $ab= p^2q_1q_2+pq_2r_1+pq_1r_2+r_1r_2; 0<r_1r_2<p^2$
$r_1r_2 \neq p$ as that would require one of $r_1$ or $r_2$ to be p
\
It thus follows that $ p \nmid ab$
How does this look?
A dense set
doesn't work
so you've found an expression for ab
ab = p*stuff + r1r2
but you've said that in order for r1r2 to be divisible by p, that would mean r1 or r2 is divisible by p
which is circular cus that's exactly what we're trying to prove
bro just stop if you keep swimming in lead rivers you will turn into stone
How come
Oh nuts
why does r1r2 = p?
why is it not the case r1r2 = 2p?
btw i've got my galois theory supervision now
so try to see if another helper can help u
also <@&268886789983436800> please can u deal with this
if you don't have anything useful to add please stop spamming the chat
Ah, good point
That would require one of the reminders to be $p$, which isn't possible
A dense set
<@&286206848099549185>
what is the question?
you want to prove euklids lemma?
no
This
this is euklids lemma
In algebra and number theory, Euclid's lemma is a lemma that captures a fundamental property of prime numbers:
For example, if p = 19, a = 133, b = 143, then ab = 133 × 143 = 19019, and since this is divisible by 19, the lemma implies that one or both of 133 or 143 must be as well. In fact, 133 = 19 × 7.
The lemma first appeared in Euclid's El...
I know
ok, so you want to prove this elementary right (without prime factorization)?
or what do you need exactly?
ok you want to continue your proof i guess
yes
you got p|r_1r_2
the idea is now that you can keep reducing mod p, do you have an idea how?
like you know r_1,r_2<p also
and assume that r_1r_2>p
then consider the minimal k such that r_1*k>p
I would like to understand why my proof is wrong
A dense set
yeah but you are using here the lemma which you try to prove
like why cant it be that $$r_1\cdot r_2 = 2p$$ with $r_1,r_2 \neq p$
cosmic
again, that would require r_2 =p
why, you are using here that the Z is a UFD, which we havent proven yet cuz this proof relies on this lemma
like we dont know that the primefactorization is unique yet
oo
like there are rings where this is false
so you have to still prove this for the integers
Aaa, rings
I literally had to prove soemthing relating to dual sided ideals today lol
yeah like Z[sqrt(-5)] 6=2*3 and 6=(1+sqrt(-5))(1-sqrt(-5)), so there your conclusion wouldnt hold
so you have to use something specific to integers, and that are often size arguments
i have to leave now unfortunatelly, sorry hope it helped a bit at least
Thanks!
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how did they find the general solution?
cause we learnt a method in which constants are infront of y”,y’ and y
what do you do if it’s not a constant in front?
Trial solution of y=X^n
Its just something u remember, when it has x infront u just try that
P much it
its also like in the screenshot u sent, u go from the equation to the characteristic equation by using a trial soln of y=e^rx
you just suggest a trial solution
@obtuse totem Has your question been resolved?
y=x^n?
n as in the highest degree of x?
No just a constant
when u sub in the trial soln y=x^n into that first image equation, youll find an equation which leads to n=2 and n=-2 which leads to ur general soln
Try it out trust its easier to understand
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u got it?
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I know how to do this question but I don't understand why my method doesn't work
I tried doing this to get
1/244sin(60) for 4sqrt3
I also got 60/360pi*4^2 =8/3 pi for the sector
Do when we consider a quarter of a circle, it is 4pi
so the shaded area for 1/4s of a circle is
4pi-(8pi/3+(8pi/3-4sqrt3))
4pi-16pi/3+4sqrt3
=4pi-16pi/3+4sqrt3
so in the whole circle,
16pi-64/3pi+16sqrt3
= -16pi/3 + 16sqrt3
which is correct
nvm I played myself
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the answer is indeed -16pi/3 + 16sqrt3 but I did a step wrong
I should have minused the 4sqrt3 instead of added it but why does that guve me a correct answer in the end
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Help me with parabolas
@oak rain Has your question been resolved?
No it hasn’t but im uses to it so I might leave the server
@oak rain Has your question been resolved?
Still no, no one fucking helps me
can u take another pic of the questions
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Guys help my homework 😭
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A dense set
Let the nullity of $T$ be $r$.Let $dim(V)=n$ Let the basis of $null(T)$ be ${e_1,e_2,\dots,e_r}$. This basis can be extended to one of $V$ , giving $\beta ={e_1,\dots,e_r,f_1,\dots, f_{n-r}}$.
\
We now show that $dim(range(T)) = n-r$. To do so we consider an arbitrary vector, spanned by $\beta$.
\
$v = a_1e_1+ \dots a_re_r+b_1f_1+b_2f_2+ \dots b_{n-r}f_{n-r}$
\
$T(v) = T(\sum_{i=1}^{n} a_ie_i + \sum_{i=1}^{n-r} b_iT(f_i)$
\
$T(v)= \sum_{i=1}^{n-r} b_iT(f_i)$
Let's suppose these vector weren't linearly independent.
\
in that case there exist non-zero scalars such that
\
$T(\sum_{i=1}^{n-r} b_iT(f_i))=0$
\
This would imply $\sum_{i=1}^{n-r} b_iT(f_i)$ lies in $null(T)$.
\
This is obviously absurd, as the vectors in the span of $f_i$ don't belong to null(T). we've thus arrived at a contradiction.
\
\
From that, we can conclude that $dim(rnage(T))= n-r$
\
From this the desired result is evident
A dense set
I feel this is missing something though
Let the nullity of $T$ be $r$.Let $dim(V)=n$ Let the basis of $null(T)$ be ${e_1,e_2,\dots,e_r}$. This basis can be extended to one of $V$ , giving $\beta ={e_1,\dots,e_r,f_1,\dots, f_{n-r}}$.
\
We now show that $dim(range(T)) = n-r$. To do so we consider an arbitrary vector, spanned by $\beta$.
\
$v = a_1e_1+ \dots a_re_r+b_1f_1+b_2f_2+ \dots b_{n-r}f_{n-r}$
\
$T(v) = T(\sum_{i=1}^{n} a_ie_i + \sum_{i=1}^{n-r} b_iT(f_i)$
\
$T(v)= \sum_{i=1}^{n-r} b_iT(f_i)$
Let's suppose these vector weren't linearly independent.
\
in that case there exist non-zero scalars such that
\
$T(\sum_{i=1}^{n-r} b_iT(f_i))=0$
\
This would imply $\sum_{i=1}^{n-r} b_iT(f_i)$ lies in $null(T)$.
\
This is obviously absurd, as the vectors in the span of $f_i$ don't belong to null(T). we've thus arrived at a contradiction.
\
\
From that, we can conclude that $dim(rnage(T))= n-r$
\
From this the desired result is evident
A dense set
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does anyone know how the ford-fulkerson algorithm works under graph theory? 🥹
@coarse agate Has your question been resolved?
<@&286206848099549185>
here's the iterations I've done but I'm not sure if I did something wrong or is this okay already 🥹
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hey guys I have a calc 3 midterm worth 50% of my grade tmr and the professor didnt explain this topic ive spent like 5 hours trying to understand can someone help me pls?
I need to be able to change the order of integration to dydzdx and dydxdz:
it gets super weird and the answer doesnt make sense to me
a GSI basically said its gonna be on the test tho and im kinda panicking
better picture of the integral
(ive drawn many pictures)
This is just normal integration but 3 times. First step would be integrating $\int_{0}^{1-y}dz$.
deepfriedrich
the problem isnt integrating its changing the bounds to dydxdz
As far as I know, you're supposed to do integrate with dz first, then dx and then dy.
$\int_{0}^{1}(\int_{0}^{1-y^2}(\int_{0}^{1-y}dz)dx)dy$
deepfriedrich
this is the full question on my practice midterm
it has nothing to do with integrating its just showing you know how to manipulate bounds
Oh, my bad I did not see that.
but the only ones I struggle with are dy[dxdz,dzdx]
getting dy first and satisfying the inequalities proves tricky
@sacred musk Has your question been resolved?
can u draw the region
@sacred musk Has your question been resolved?
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The problem is here
what's a "chain"?
Chain rule
Yes
oh wait that's the answer
Happens.
The problem is here
Ah, I'm not good at reading handwriting but I can try.
Ok
There are some simplifications you can do
nothing more than that.
Like cancel out x from numerator and denominator
so the x^2 from the numerator will be gone?
Look here, it's not possible to cancel out x^2.
So how do I get the second form?
In this
Take x common from numerator
No.
Like this
$x(x(2e^{2x}-2e^{-2x})+2e^{2x}+2e^{-2x})$
You can do differentiation, this shouldn't be a big deal, right?
Differentiation of?
Differentiation is another name for derivatives.
I missed the 2, my bad.
deepfriedrich
so the x^2 is the x(x?
$\frac{x(x(2e^{2x}-2e^{-2x})+2e^{2x}+2e^{-2x})}{x^4}$\
\
$\frac{2xe^{2x}-2xe^{-2x}+2e^{2x}+2e^{-2x}}{x^3}$
deepfriedrich
Ohhh
Then you take 2x common and simplify further.
ok ok
$\frac{2(e^{2x}(1+x)+e^{-2x}(1-x))}{x^3}$
deepfriedrich
This is after clubbing e^{2x} and e^{-2x} terms together.
Oh okk
Wait how?
See what terms have e^{2x} multiplied to them
2xe^{2x} and 2e^{2x}
Then take e^{2x} common
e^{2x}(2x+2)
2e^{2x}(x+1)
I still don't get it, I'm sorryyy.
I can't spoon-feed harder than this </3
Okkk
deepfriedrich
Yes
This and the example I sent are the same on a fundamental level.
Just imagine e^{2x} instead of "b" here.
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it is like the number of positioning 6 object in 6 different places
divided by the number of symmetries that the cube has
so 6!/3!?
Well each of the six sides can be up top
But for each side being up top you can rotate the cube along its vertical axis
4 times
how do u even calculate it
A position of the cube is defined by bottom face and a rotation of the z-axis
With then different faces being in the front each time
so it seems like 6*4
yea
Like I described above. For any of the possible 6 sides on the top there are 4 rotations. Meaning 6*4 rotations in total
oh
so every side is symmetrical to other
then how is it not 6*6
With a given side up top, how would you rotate the cube six more times?
oh so i get it rotational symmetry is when u rotate an object and still get the same shape
After rotating
Sure, that’s the same as 6!/(6*4)
after painting the first side(be any) take the opposite side and you have 5 ways to do it and the rest is circular combination (n-1)! I didn't get their method
this is what it says
This is basically the comprised version of the 6!/24 explanation.
We say we start with the first color. For the opposite face there are 5 colors and for the other for there are 3! Ways to do it. Since the starting color doesn’t restrict our options, 5*3! Must be the solution
I don’t really like that explanation though, I find it too unconvincing
shouldn't the first side have 6!
how is it 1
You start with the first color, not the first side
unfortunately that's what i have to write in my exam
Shouldn’t this be fine too?
my teacher is a .... he will probably cut my marks
Doesn't allows to use different methods
🤡
Yw
have a good day
You too
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I want to prove the following lemma
I actually have a nice proof of this at hand
Well actually, only in one direction i suppose
As in cgcd(a,b) \geq gcd(ca,cb)
Yea sure
or something like that
g(ac,bc) | c*gcd(a,b)
May be a bit restricted though, depending on what you’re allowed to assume
take $d = gcd(a,b)$ and $D = gcd(ca,cb)$
rafilou is not not born in 2003
Yeah, I know how to do that I think
For bezouts, I was thinking $k_1a+k_2b = gcd(a,b)$
A dense set
we now multiply across by $c$ to obtain
A dense set
$k_1ca+k_2cb=cgcd(a,b)$
A dense set
but k_1(ca)+k_2(cb)=gcd(ca,cb)$ for some choice of $k_1,k_2$
A dense set
Compile Error! Click the
reaction for more information.
(You may edit your message to recompile.)
therefore $gcd(ca,cb)=cgcd(a,b)$
This one is the other direction
A dense set
the problem we run into is proving that the K_1, k_2 are the same
alternatively, you could use the fact that the gcd is the only common divisor that can be written as a linear combination
for d >= 0, d = gcd(x,y) <=> d|x, d|y and d = ux+vy
Hmm
Thanks!
thanks
One thing I always like to point out here is that the 4th line follows only from the cancelability of c (I find that part is hard to spot)
So c can’t be 0 here
Let me try now :
Let gcd(a,b)=d
$d \mid a \land d\mid b$ by definition
\
As proven earlier $ca \mid k \land cb \mid k$
\
It also follows that $ca \mid ck \land cb \mid ck$.
\
\
It thus follows that $gcd(ca,cb) \mid cgcd(a,b) \implies gcd(ca,cb) \geq cgcd(a,b)$
A dense set
We now attempt to prove $cgcd(a,b)\mid cgcd(ca,cb)$
A dense set
What’s k here?
@twilit field Has your question been resolved?
My bad, meant to write $d$
A dense set
Let $gcd(ca,cb)=k$ . By definition $k \mid ca \land k \mid cb$. We let $gcd(a,b)= l$. We wish to show that $ cl \mid k$
not sure this is what you want
because proving what you wrote would imply gcd(ca,cb) | gcd(a,b)
A dense set
We prove this via contradiction
We assume that $ k \nmid cl$
so $k = clq_1 + r; 0<r<cl$
A dense set
this is still going?
I was eating dinner until a while ago
We start by dividing across by $c$ . This gives us $\frac{k}{c} = lq_1 + \frac{r}{c}$
A dense set
We know that $c \mid k$. It thus follows that $r$ is a multiple of $c$ or is 0
A dense set
Okay, now what
<@&286206848099549185>
Let $gcd(ca,cb)=k$ . By definition $k \mid ca \land k \mid cb$. We let $gcd(a,b)= l$. We wish to show that $ cl \mid k$
A dense set
From this we can conclude that $ l\ mid a \land l\mod b$
so $ca=kq_1; cb = kq_2$
\
We also know that $a=lq_3; b=lq_4$
A dense set
ooh
okay
thanks
so just to be sure we let d be the gcd of (a,b)
so $d \mid a\land d \mid b$ . We then let $ D \mid ca$ and $D \mid cb$ . It also follows that $cd \mid ca \land cd \mid cb$
A dense set
so $ca=dk_1;c b=dk_2$ . We also know that $Dk_3=ca; Dk_4=cb$
A dense set
It thus follows that $dk_1=Dk_3$; $dk_2=Dk_4$
A dense set
A dense set
Let's assume that $cgcd(a,b) \nmid gcd(ca,cb)$
A dense set
$cl \nmid d$
A dense set
so $d = clq_1+r$
A dense set
dividing across by $c$, we find thet $r=0$ or $r$ is a multiple of $c$
A dense set
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let $\alpha >1$. Show if $|f(x) \leq |x|^{\alpha}$, prove $f$ is differentiable at $0$
A dense set
So here, I'll have to prove continuity first, do I have to use $\varepsilon-\delta$
A dense set
LHL=RHL = F(x)
Why do you need to prove continuity first?
Only then can I even consider it being differentiable
I don't see why
I need continuity to obtain $f(0)$ too
A dense set
A dense set
that gives me $f(0)=0$
A dense set
Just apply the definition of differentiability
Yeah
realised now
We have $|f(0+h)-f(0)| \leq |h|^\alpha$
\
We thus have $\abs{\frac{f(0+h)-0}{h}} \leq |h|^{\alpha -1}$
A dense set
We now take the limit of both sides as h tends to $0$
A dense set
$\lim_{h \to 0} \abs{\frac{f(0+h)-0}{h}} \leq \lim_{h \to 0} |h|^{\alpha -1}$
A dense set
It's apparent from this that the lhe derivative is $0$, and that the function is differentiable
A dense set
Is this enough
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mfs i need help
Maple Grove High School is designing an L-shaped walking path for their campus. The longer straight section of the path is 4y+7 meters, and the shorter section is 3y−2 meters, where y represents a variable length. The width of the path is consistent at y+1 meters throughout. Write a simplified polynomial expression to represent the perimeter of this L-shaped walking path.
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A sphere of solid material of specific gravity 8 has a concentric spherical cavity and just sinks in water. What must be the ratio of radius of cavity to that of outer radius of the sphere?
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What did I do wrong here to get the incorrect solution pi/2 + npi instead of pi/2 + 2npi (more specifically, why can't n be an odd integer in npi)?
Given: cscx + cotx = 1
1/sinx + cosx/sinx = 1
cosx + 1 = sinx
cos^2 x + 2cosx + 1 = sin^2 x
2cos^2 x + 2cosx = 0
2cosx(cosx + 1) = 0
x = pi/2 + npi, pi + 2npi
When you square both sides, you introduce new answers to the question. That means that you have to check the answers you get.
For example, say I have (x-1)=4
(x-1)^2 = 16
When I factor and solve, I get x=5 or x=-3
but -3 was not an answer to the original question
how can I get the right solution instead
where even is your problem
What you did is good. You just need to check your answers.
cscx + cotx = 1
they say that's a given?
That’s the problem
that's an equation. what are you supposed to calculate
x
I know it's not the best way to pose a problem, but you can tell from context
yea mb
unless you're not actually asking and you're just trying to get GoldenTrash to format better
I just listed my steps afterwards
U applied the wrong formula
By comparing with Cos theta = Cos Alfa
We get, theta = 2nπ + alfa
wait sry where
Check ur last step
By comparing with Cos x = Cos Alfa
We get, x = 2nπ + alfa
what is alfa in this case
but 0 comes every pi interval
I don’t understand why to compare cos theta with cos alfa
Replace theta with x
It's a formula
R u from India?
no united states
Ohh so ig ur textbook can have different formula
but 0 comes every pi interval, so why 2npi
no
Any textbook?
no
n belongs to integer
Yess
U can check last second line where we took 2 common
@marsh veldt Got the reason?
why doesnt pi/2 + npi work for the equation if the solution for 2cosx = 0 is pi/2 + npi though
Is π/2 + nπ correct answer
no
no worries, but the answer is pi/2 + 2npi
I was confused on how to obtain that answer
Wait I am sending u the solution
In my country, it's completely based on formula
Please replace theta with x cuz we use theta mostly so it's in my habit 😅
but the correct answer is pi/2 + 2npi
R u sure?
Ig now I am unable to solve it
Can u send me the graph
Do u know the concept behind this
Ig I'll take time to understand this 😅
ok ty for your help
Sorry sorry
I am unable to help
Please reopen ur question
But thanks a lot u helped me clearing my concept ✨
yea np ig
<@&286206848099549185>
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@marsh veldt Has your question been resolved?
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How do I find where the function is increasing and decreasing?
I found the derivative:
you can also use |x| and think about how the transformations affected f(x)
So in a sense, I don't rlly need the derivative?
nope
Hmm... how would I determine them using the derivative tho
Yeah I know but I'm just having trouble
Because how I do it is i find the critical point then determine how the function behaves using nearby points
its so much easier to do the derivative by cases instead of this inconvenient thing
What do you mean by cases?
just do cases depending on whether the inside of the absolute value is >=0 or not
ok
bacc (unhelpful)
Ahh I see
also your derivative isnt correct
okay let me try
Let me work on that
Would this be the derivative?
or just -2?
they are telling you to take the deriv of a linear function
you need to apply the piecewise defn of absolute value
|y| = y if y>= 0
ohhh i see
|y| = -y if y < 0
it's correct
you neglect the denominator since at x = 3 is not differentiable anyway so you really solve -2(x-3) >= 0 and -2(x-3) < 0
@mental bone Has your question been resolved?
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$\sin^2 x = 1 - \cos^2 x$
timuko
for the rhs?
Yes
is it easier from there
Maybe try using complex numbers
i have not learnt them
$\cos(3x)=\cos(x+2x)=\cos(x)\cos(2x) - \sin(x)\sin(2x) = \cos x(2\cos^2 x - 1) - 2\sin^2 x \cos x = 2\cos^3 x - \cos x - 2\cos x(1 - \cos^2 x) = 2\cos^3 x - \cos x - 2\cos x + 2\cos^3 x = 4\cos^3 x - 3\cos x$
timuko
You could do this
Or
You could use the property
CosA +CosB = 1/2 Cos(A+B/2) Cos(A-B/2)
A being 3x and B as 5x
Wow, I completely forgot about this property
You could then use Cos(2x) = 2cos^2(x) -1
Yes
It's a sum
$-\frac{1}{2}(\cos 3x + \cos 5x)$
timuko
It reminds me of half-angle identity of $\sin \frac{\theta}{2}$
timuko
Like $\sin 2x = \pm \sqrt{\frac{1-\cos 4x}{2}}$
timuko
yea i see it
Here is a cheat-sheet:
i know them
.
like
First your x would be 2x,if that made any sense XD
2cos^2(2x) - 1
Yeah
does the minus sign affect both
like
cosx*(1 - 2cos^(2x) - 1)
or cosx * (1 - 2cos^2(2x) + 1)
honestly
this
You are right
1+1 right?
Good
so
Go on
do i use
cos(2x) = cos^2(x) - sen^2(x)
or ig i could take the 2 out
2(1-cos^2(2x)
and change that to sin^2(2x)
Rather than using cos2x equals 2cosx minus 1
Using cos2x equals 1- 2sin^2 x eliminates the 1
oh yeah
but we get to the same thing anyways
or not
i think not
ok
cos(x) *(1 - 1 + 2sin^(2x))
oh we do
cos(x)*(2sin^2(2x)
Sin2x can be expanded to?
cos(x)*(2.2sin^2(x)cos^2(x)
Yep
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This is the one issue I have is finding the asymptotes, I tried y = 900, y = 0 and was wrong? not sure what I am missing
you have written the equation of a vertical line
what happens as t tends to infinity
specifically to the e^(-0.1692t)
oh actually
i see, did you actually write 'y'?
try p
Originally I did because I was listing the asymptots at y = 900
I did t = kinda as just a shot in the dark
ohh
so would it be p(t) = and then where the asymtots cordinate is?
like p(t) = 900 yeah?
you can skip the t but yeah
ohh ok ok
p=900, p=0 should be okay
wait no
the 0 is fine, the 900 not
sorry ignore that, got confused
youre good
So my original listing of 0 and 900 was right I was just missing p=?
yup
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hi can someone explain how for problem c, it’s 42 seconds? i dont get it 🥲🥲🥲
Why did you label the second peak 42
@meager plover Has your question been resolved?
that’s the x-value
How?
for c or just on my graph
Your graph
the max distance is 25 yds, and michael reached 25 yds in 21 seconds
since the graph is in a cycle, the period is 21 seconds. so he completed 25 yds for the second time in the timeframe of 0-42 seconds
the period is the distance between the peaks
that’s just when he completed his first lap
The 42 should be when the distance returns to 0 first time
The period can also be from 0 to 0
Which is 42
no bc after 21 seconds, he reached maximum distance
after another 21 seconds, he reached the max distand again
21+21=42
Max distance?
pool is 25 yds long
Yeah it takes 21 seconds to swim 25 yards
And then 21 seconds again to return from the other side to starting point
Hm
because the answer key said point D is 84 seconds
Wait
Ohhhhhhhhhhh
no youre right
i get it now
sorry i thought for whatever reason, 42+21=84 😅😅😅
Wait but i dont get why it takes 42 seconds to get from point A to point C
Because that's a period
Oh so the period is actualy 42 seconds
😭😭😭
Ok my brain just doesn’t wanna function simple math
ok ty
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help me
first part is just solve for roots and factorise over the real field noting cos4π/5 = -cosπ/5
how do i find cosπ/5 and cos2π/5
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
i tried SOR and POR of the quadratics but that doen't really help me
with the 2nd quadratic
cis2π/5 + cis(-2π/5) = 2cos2π/5
but that's just a true statement cuz LHS is 2Re(z)
similar with POR
Consider the sum of the roots from all three factors. What must this sum be equal to (||consider the left hand side||)?
ohh
1 + cis(2π/5) + cis(-2π/5) + cis(4π/5) + cis(-4π/5) = 0
1 + 2cos(2π/5) + 2cos(4π/5) = 0
cos2π/5 - cosπ/5 = -1/2
then do i use POR ?
oh so i do cos(2π/5) = 2cos^2(π/5) - 1
sub into the other equation and get a quadratic
solve then choose whichever solution is right?
ok i got it now
THANK you
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could someone explain how to go from that top right equation to the bottom one?
$\frac{y-3}{y-3} + \frac{3}{y-3}$
knief
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The perimeter of a rectangle is 80dm. The width is 1 more than 1/2 of the length. Find the length and the width of the rectangle.
do I use substitution
what’s the formula for perimeter of a rectangle
P = 2(L + W)
half of length
yes then express W in terms for L
how
^^^
L/2?
Yeah
yes L divided by 2
Length divided by 2
which is half the length
can you show it, i don't understand in terms of text
Ok what do you not understand
all of it, can you start again, im lost
If length was 4(say) then width will be (half of 4) + 1
But length is a variable here which we have to find so we denote it with L.
Because we have already established that W is equal to L/2 +1
Then because you multiple everything by 2
You get this
Then you add them together
but it's only 2L
Do you know how to expand brackets?
Look at the very top line in the photo
Everything in between the brackets have to be multiplied by the number directly next to the brackets
So multiply everything by 2
yes
just got a lil confused with this, but I understand it
so what's the length and width
@pseudo moat Has your question been resolved?
this will become 3L = 80-2 which will become 3L=78 then divide both sides by 3 to get L which will be 3L/3 = 78/3 which will be L=26
is that correct
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hello, i dont know how to approach this following problem: in graph theory, let us describe a simple graph of n vertices and m edges assigned an integer value from 0 onwards. in each operation, when you chose a pair of connected vertices, one minuses 1 from one vertice's value and adds 1 to the other. call the task winnable if it is impossible after applying any number of iterations no two linked vertices are both 0, and let the smallest sum across all the n vertices be k. find all possible values of k, given m and n
i tested it for small values of n like 2 and 3, but for greater than 3 testing becomes difficult and ideas need to be come acrossed
@nova pike Has your question been resolved?
<@&286206848099549185> Anyone good at graph theory or know any techniques for solving this problem, it would be would be much appreciated if you could help me
so you have a graph with n vertices each numbered from 0 to n-1, and at each step you can take two connected vertices and subtract 1 from one vertex and add 1 to the other?
You will need to iterate through all the vertices of the graph making sure no connected vertices (having same parent) are both 0
Disjoint Set with specific optimization can help you with that traversal
well it seems like if the initial sum is fixed, then the sum is always the same since subing 1 and adding 1 keeps the sum constant
Sorry I did not mean this. We can have values of each vertex any integer from 0 and above. For example with four vertices, we could have values 0, 1, 3, 1, etc. also I am not the best at graph theory, so feel free to correct me anytime
Yes, exactly
i see
I’m sorry, how would we do this?
i think he means a search with a computer
yes
I can write a program in Java that can help you solve this
but the problem is I don't understand the point of this problem?
What is it trying to achieve ultimately??
well then it seems like the graph part of the problem is not relevant, all that you need is the initial sum of the vertices
also fyi, a forest is a set of disjoint trees, which i assume is not what you are talking about
yes, and a tree can also be classified as a type of graph
well im saying that it seems like he is ignoring the forest part of the statement
That would be great. I don’t know how to script things
so then the minimum sum is 0, and the maximum is n(n-1)
I think this is what I am talking about. The reason why I am not that great with this problem is because I tried to convert another problem in terms of graph theory which become this problem. Due to the original problem conditions, I figured that they only allowed ‘forests’ as graphs
so it's important that the graph be a set of disjoint trees?
Yes. The original problem had that each edge is connected to some two vertices and each pair of vertices is connected by one edge at most
that's just a simple graph
not necessarily a tree
or a forest
simple means that there is at most one edge between vertices and each edge is between exactly two vertices like you said
Ah, I’m so sorry, then I meant only simple graphs work for this problem, not forests
ok, then if i understand correctly, you need to find all possible k for all winnable graphs with n vertices and m edges
then it's a bit tricky because for some values of m, there are no winnable graphs
Yes
namely if m = n(n-1)/2, so that the graph is a complete graph
then, you can always make two of the vertices 0
im not sure if there will be a closed form
Yeah
I tried working with smaller n and building my way up, but it becomes hard to search for n>3
What happens if we fix a m and n? Then would we be able to compute all possible values of k easily?
Is the following graph winnable? (0)—(1)—(0)
wait but now it seems like any graph with three vertices that are connected in a row is unwinnable
no, as you can move the 1 to the end
Yes
ok, then it seems like there are actually few values of m so that a graph with n vertices is winnable
No, it’s not winnable which bair explains why exactly
okay then yeah i agree with this
yeye you got it
Interesting. How exactly?
so i think when m < n/2, there are n(n-1) possible values of k, and 0 otherwise
"few" meaning not all of them, only for m < n/2
because when m > n/2, then there three vertices that are connected
which means that the graph is unwinnable
so if there was a graph with 100 vertices and 1000 edges, then there does not exist such graph?
right, because there are three vertices that form a connected component
and therefore, if the numbers are x-y-z, then you can make (0)-(0)-(x+y+z)
actually a funny edge case is when m = 0, then you can have n(n-1)+1 values of k
Wait, how is this possible?
Interesting, how is that so?
well can't you first move (0)-(x+y)-z and then (0)-(0)-(x+y+z)
when m = 0, no vertices are connected, so you can make every vertex have a value of 0
but if there is at least one edge, then the sum has to be at least 1
Oh, I think I made also a terrible mistake in what I was trying to say which makes the problem much more complicated. The person that is making each iteration wants there to be a 0-0 but the vertices move in a way that always try to avoid this
the vertices move??
how
do you mean the vertices are arranged so that the graph is unwinnable?
Yes, I mean this.
Im so sorry, I really wanted to convert the original problem into a graph theory one
but then the problem is even simpler, then if m>=2, then there is always an unwinnable graph
so for m>=2, the only value of k is 0
and when m=1 there are n(n-1) values of k
and when m=0 there are n(n-1)+1 values of k
can you send the original problem, maybe it will help makes things clear
Yes, I’ll send it
I thought replacing 100 with n and 1000 with m would help solve the problem in general
oh i see, so merlin gets to chose the edge, but not the direction in which the wise men move
this is quite different to the earlier statement
Merlin does not matter. It’s just like a person choosing a corridor and asks one of the people from one of two rooms to go through the corridor into the other room
I understand, I’m so sorry. I tried to rephrase the problem in terms of graph theory, but to no avail
yes, but the point is that we cannot have the situation from before, when (x)-(y) became (0)-(x+y), since the wise men could just keep moving back and forth
Yeah, I was wanting to tell you this but couldn’t express it properly
hmm, then it is a tricky problem, let me think
alright, thank you for your time and patience
well im very stuck, it seems like it highly depends on the structure of the castle
one idea is to alternate the parity of every room
since then, the parity of each adjacent room will swap, hence not both can be 0
but this is not always possible, depending on castle layout
you would need a bipartite coloring
wait, wdym by this?
like if i have (even)-(odd), then no matter which way the wise men go, we will get (odd)-(even)
wait but then the parity will be the same on the other side
so this doesn't work
yes, I get this, but why different parity?
don't worry, it doesn't make sense
ok, it is giving me a lot of trouble, i would suggest pinging helpers again, or asking in #discrete-math , or asking again when more people are awake
Oh ok, thank you for your time and help. I was also thinking of converting this into a string of numbers followed by suitable operations, but idk where that would lead to
Thank you so much, and sorry for causing such a big inconvenience
np, next time i would just suggest sending the original problem first
and then saying how you reformulated the problem
Oh ok
@nova pike Has your question been resolved?
<@&286206848099549185> here is the problem. instead of 100 rooms, i tried breaking it down into 2, 3 etc. but from >3, it becomes hard finding the best and minimal possible construction
i have two questions:
- whats the meaning of "every minute" as there is no other time relevant information in it? would it be the same if its just "every thirty seconds" or "every hour"?
- if merlin has choosen a corridor and a wise man psssed along it, would it be a simple strategy if the wise man will go back?
for the first question, yes it would be the same. it would just be considered every single iteration. for the second question, that is if merlin has chosen the same corridor again, then yes, a wise man can go back
does this mean the wise men can only move after a choice of merlin?
yes, and only one wise man each iteration
ok, then i do understand nothing. whats the meaning of "the wise men needs to scatter across the rooms in a manner they wish"?
if only one man can move and only in the corridor which is defined by merlin i cant see a "a manner they wish"?
they do this btw before merlin starts picking a corridor
its like saying if you have a_i be the number of wise men in the ith room, then you have the sum of all a_i for i = 1 to n be the number of wise men in total
<@&286206848099549185> if someone could help with this problem (which looks like theres some graph theory in disguise), that would be much appreciated
Does Merlin win if there's no wise man in a room but there's one in the other
Not necessarily. Merlin wins if at the end of any iteration there exists a corridor connecting two rooms both with 0 people in them