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yes because
you're subtracting 2 two times on one side, and one time on the other
theres an imbalance
So I am not supposed to -2 to both +4 and 3 i only choose one of them right?
yes
how do i know which one to choose
okay cool how do close this
.close
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hello can someone help
@brazen stump Has your question been resolved?
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Hi, i hope you dont mind me asking this physics question here
but wouldnt the answer to question 1 be: The results would be less accurate because 100g is a light weight and the spring balance wouldn’t measure it accurately this is due to the fact a person must read the pointer’s position. This can be difficult if the pointer only moves a small distance. The measurement uncertainty becomes larger.
@rain sentinel Has your question been resolved?
Your approach is on the right track but not reasoning
Definition of accuracy is what matters the most here
In the question,they have defined accuracy as the lowest percentage/numerical value of relative error,which decreases with decrease in absolute value
So when you actually lower the exact value,absolute error lowers down too,giving you more accuracy
@rain sentinel Has your question been resolved?
so it should become more accurate with 500g
If we were to define a relation between mass of the sample and accuracy in this case,then it is inversely proportional
so im incorrect?
what is experiment 1 here
like what are you trying to measure
If it's the mass then maybe ts could help
here i have taken the error for the weight to be 0 since we have been given precise weights
so the error in m is directly proportional to the m assuming the error in g is constant for both cases
so as we increase the weight the error increases as the mass increases
If you are calculating weight instead of the masses then ts statement would be valid as well
@rain sentinel Has your question been resolved?
The aim of this lab is to calculate and predict the loading and reaction forces required to keep a real-life system in static equilibrium
im measuring the force not mass

ts is what would be applicable here then

Experimental accuracy – if experiment 1 were repeated with 100g weights instead of 500g weights, would the results be less or more accurate? Why?
so this is the question
ye so as you increase the. mass of the system you can see the error in weight or in turn force needed to be in equilibrium increases
which is not ideal so 100g would be more accurate
...

so it would be more accirate with 100g
obviously i cant write what you said down
According to the results from experiment 1 and by comparing between thetheoretical and measured results for both 500g and 100g, it has been shownthat using the 100g weights gave out more accurate results. This clears out thatusing less weights produces more accurate results. This could be because theweights we used were just 10g, and using a large amount of them could causean increase in the errors or uncertainties giving out less accurate results.
so this is the valid answer
not this: Smaller weights produce smaller measurable effects, so the same measurement uncertainties have a greater impact on the final calculated results — making the experiment less accurate.
@rain sentinel Has your question been resolved?
@rain sentinel Has your question been resolved?
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5 people sat in a room with 5 chairs, and there are 2 of them, A and B. they were asked to come out of the room. how many ways could they sit upon their return, given A and B didnt sit in their own previous chair?
.close arghhh im stupid
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why did i use 5!-7 when it shouldve been 5p2-7
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Let $p,q,r$ be roots to $x^3-7x^2+1=0$. Find
$$\sum_{\text{cyc}}\sqrt{\frac{(p^2+1)(q^2+1)}{r^2+1}}$$
ihave<skissue>
yeah idk status 1
@jagged flare Has your question been resolved?
hmm, maybe firstly you can consider making a polynomial where the roots are p^2+1, q^2+1 and r^2+1
@jagged flare
i thought of that, but wouldnt you get square roots
well the easy way I would think is to produce the companion matrix $A$ for the polynomial, then computing $\det(xI-(A^2+I))$
Element118
havent learnt anything that you said so this gonna take a while
another way is probably whack vieta formulas
ew
which I would think it is less easy
im open to new methods
well ig companion matrix it is https://en.wikipedia.org/wiki/Companion_matrix
In linear algebra, the Frobenius companion matrix of the monic polynomial
p
(
x
)
=
c
0
+
c
…
so basically the companion matrix is a matrix with eigenvalues equal to the roots, but using it, you can figure out the eigenvalues of A^2+I
whats an eigenvalue
mm ok so an eigenvalue is a scalar that multiplies the eigenvector such that it equals an n×n matrix multiplied by the eigenvector
Wdym, if you find the polynomial in terms of x²+1 as you said then it's an immediate application of vieta
wait I guess I misunderstood
almost immediate
yeah ok
Anyway you don't need those things to find that polynomial
I mean I know you know but here it's simple enough not to use them
you can just do it by finding the constants seperatly as well ,using the root relations
ok tldr, for a square matrix there exists an eigenvector and eigenvalue so that matrix×eigenvector=eigenvalue×eigenvector?
wdym?
yk sum of roots is -b/a and all that
yeah how do you use that
so sum of roots of an equation with roots p^2+1 ..... would be p^2+q^2+r^2 + 3
which you can find out
not that there exists, but you need algebraically closed field for it to exist
whats a field and what does it mean for it to be algebraically closed 
that's just how eigenvectors and eigenvalues are defined (though you need your eigenvector to be nonzero)
yeah ok im leaving linear algebra for college 

field, like rationals, reals, complex, you can add subtract (commutative) multiply and divide. Basically complex numbers form an algebraically closed field, that is, every nonconstant polynomial has a root
ohhh like that
ok hold on thats interestinf

then do it
you can find p^4+q^4+r^4 using the newtons method
p^2+q^2+r^2+3=(p+q+r)^2-2(pq+pr+qr)+3=52
it's a bit bashy but it works
err newton girard iirc?
i think ye
that one
basically x^4 = 7x^3 - x
better than learning matrices then the meaning of eigens on the fly tbh 
In case you wanted to see how to do this, notice that ||you expect it do be a 3rd degree polynomial in terms of y=x²+1 so you probably want to find it through squaring the equation you have and get an even polynomial. You can fix the odd degree terms using x³=7x²-1||
P_4=e_1P_3-e_2P_2+e_3p_1
Actually ||if you square it in the right way you get an even polynomial right away||
e_1=7 e_2=0 e_3=-1
P_1=7 P_2=7×7-0×2=49 P_3=7×49-0×7+(-1)×3=340
p^4+q^4+r^4=P_4=7×340-0×49+(-1)×7=2373
err thats alot
actualy where does this even come into play
to find p^2q^2+...... term
good point
(p^2+1)(q^2+1)+(p^2+1)(r^2+1)+(q^2+1)(r^2+1)=p^2q^2+p^2r^2+q^2r^2+2p^2+2q^2+2r^2+3=107+((p^2+q^2+r^2)^2-(p^4+q^4+r^4))/2=107+(331/2)
its not an integer??
i'm thinking it has to be an integer
ye
because my method would produce an integer
so that means the computation went wrong somewhere
hmm
imo you should just simplify ts expression
prolly here somewhere then
you would get (p^2+1)(q^2+1) + ..... in the numerator
and the square root of the product of all three in the denominator right
yeah that's one way to simplify it
your values are sorta wrong here
3 + 2(p^2+q^2+r^2) + (p^2q^2+....)
that should be what you get
whats what i got?
and all of these should be integers 
i just grouped em for you
tell me what values you found
yup you can do that as well
3+2(49)+(331/2)
the last bit is the problematic
how did you get 52 shoudnt it be 49
(0)^2-2(-1)(7)=14=p^2q^2+p^2r^2+q^2r^2
so the last bit would be ((49)^2-2373)/2=34
but why did i get 14 here
because thats the answer ....
it's 14
14/2 actually

huhh 😭
so this would be 3+2(49)+(7)?
yup
now for the bottom part take -1 common from each term
-(-1-p^2).... thats what you will get then right
it can just be seen as inserting -1 into a cubic polynomial with roots p^2,q^2 and r^2
then multiplying the result by -1
that should be it
huh sorry what
a cubic with roots a,b and c can be written as (x-a)(x-b)(x-c)
inserting -1 in it would give you (-1-a)(-1-b)(-1-c)
which is the same term as above

I'm talking about the denominator of the orignal problem yes
oh like after you combine them?
youll be left with this in the numerator
and sqrt((p^2+1)(q^2+1)(r^2+1)) in the denominator right?
ye
and how do you make the polynomial with roots p^2 q^2 r^2 again
oh wait
sum is 49
yup
the product sum thingy is 7 (?)
yup two at a time is 7
product is 1
yup
so t^3-49t^2+7t-1 has roots p^2, q^2, and r^2
yup
t^3
:p
subbing t=-1 we get -58
yup
since theres a - the denominator is sqrt(58)
now multiply that by the -1 we took out
so 108/sqrt(58)
-1-49-7-1=-58?
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This is very unordinary but I have a puzzle that works like in the video and I really need help.
I am looking for a password, 1 word or could be multiple
This is a tesseract, 5x5 Rubik's cube style. Where each letter moves according to the directions.
Any help would be much appreciated
it seems each face is an independent puzzle
Yes and once the timer resets the letters get randomized
idk what the solve state is
This is more on the cryptography side
I was thinking a Polybius Square looks like it
That has the I/J letters
idk, where is this on
is this a webpage or something
it's a webpage, you can view source or something
the letters don't look important since they are random
so idk what's there to look at
Well they should unlock the locked layer if you put them in the right order
And could give the English key for the password
@winter grail Has your question been resolved?
What program is that
It's just a js someone made
Needs to be solved
@winter grail Has your question been resolved?
@winter grail Has your question been resolved?
Any idea?
if this is a game you lowkey might have better luck decompiling it and inspecting its code
😭
if this a web game you should try to use inspect element to analyse it more
can you send us the file?
Its a webgame a puzzle hunt
Sadly not allowed to use the console
Considered "cheating"
Its an interactive js code cube
Looking to get a password out of this, if you sort the letters in the right way you can unlock the lock I believe
well i was thinking about using a script to automate things
i guess that wouldnt be allowed?
nvm now that i think about it, it would just be easier to copy the faces into a program and then perform some scripting on it rather than interact with the webgame directly lol
can you show us a full set of 5 faces?
it's a little hard to tell from that video
it could be a playfair cipher https://en.wikipedia.org/wiki/Playfair_cipher
The Playfair cipher or Playfair square or Wheatstone–Playfair cipher is a manual symmetric encryption technique and was the first literal digram substitution cipher. The scheme was invented in 1854 by Charles Wheatstone, but bears the name of Lord Playfair for promoting its use.
The technique encrypts pairs of letters (bigrams or digrams), ins...
@winter grail Has your question been resolved?
Its polybius square confirmed
And the task is to sort the letters in abc format
But doing that for all 5 faces manually under 10 minutes is very hard
you could use a program/script to do it for you
Got 10 minutes to solve all of this
Its got an anti cheat system
Unless you know a way to bypass it.. 👀
input in each of the 25 characters in each face
and generate the optimal solving input
by hand
you could potentially optimise it further by reading each face with ocr
not sure how it would fare, given that there is a lot of 'noise' due to the cube's transparency
Yea tried ocr tools but it couldnt read it
Idk i can type out one face in under a minute
If you can make a script, how could you run that without the console or terminal
oh yeah wdym "abc format" like alphabetical order?
If I knew the exact steps for all faces I could do them under 10 minutes
what does that have to do with a polybius square btw
Just the I/J I guess
bruh
It's called the Polybius Cube in the source
Yes
Once you solve one face it turns blue
5 faces under 10 minutes
You have about 2 minutes per face to solve
If anyone else wants to try this, here's the problem formalised a little:
You have a square face (say, the input square):
[ 0 1 2 3 4
0 ['D', 'U', 'Z', 'I', 'O'],
1 ['S', 'V', 'C', 'A', 'W'],
2 ['G', 'M', 'P', 'F', 'Y'],
3 ['N', 'R', 'T', 'E', 'Q'],
4 ['L', 'X', 'H', 'B', 'K'],
]
On each move, you can perform two things:
- Rotate a row i of the square by n places rightwards (positive direction) or leftwards (negative direction). Denote this as r(i, n) where i \in {0, 1, ... 4} and n \in {1, 2, 3, -2, -1}
- Rotate a column j of the square by n places rightwards (positive direction) or leftwards (negative direction). Denote this as _c(j, n) where j \in {0, 1, ..., 4} and n \in {1, 2, 3, -2, -1}.
A row, or column, will always wrap around itself.
Your goal is to get the square into the form
[
['A', 'B', 'C', 'D', 'E'],
['F', 'G', 'H', 'I', 'K'],
...
]
with as few moves as possible, while still maintaining a decent execution time.
Note that the letter 'J' is missing.
i know this is solvable by a greedy algorithm, however the move sequences will be pretty long
for a more optimal move sequence, i think maybe some sort of A* might help? but i'm not all too familiar with graph algortihms so...
Yes
Now do that for all 5
And it gets randomized each time
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What is wrong?
,rccw
how did you simplify $\frac{a^{6/4}}{a^{-2/4}}$ to $a$?
Ann
and for that matter how did $\frac{b^{5/4}}{b^{13/4}}$ become $b^{-8}$
5/4 - 13/4 is also not 8
Ann
a^4/4
yeah sign error as @worldly mesa just said
It’s
2(a^2) now
It’s easier
To mark like that
5/4 - 13/4 = (-8)/4
Which is b^-2
@tired walrus
yes
Ok
I mistook it then and just pasted -8
I’m a little bit confused
Why isn’t it (2a^2)/b^2
@tired walrus
that two was in the denominator, and you weren't supposed to pull it into the numerator
also i admit i didn't notice what happened to the 2 because i was trying to help you get the exponents right
but the 2 was in the denominator and it stays in the denominator
How do you get a^2 from this equation?
I don’t seem to get a^2 but a @tired walrus
you're making the same sign error with the exponents on the a
a^(6/4 - (-2/4))
is a^(6/4 + 2/4)
So if it’s
1 -(-1)
It’s 1+1
Cause - is near the bracket
So you change the numbers
Just like
negative times negative gives positive, yes
no, 9(5+x) never happens in yours
5 - 9 - 5 - x
simplifies to -9 - x, and that's that
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hii I need help on how to convert decimals as fractions
does that thumbs upmean youll help me? sorry im new
yeah
ahh ok so like how do I do it. when im in class i get on the calclulator 0.75 but how am i supposed to know thats 3/4
generally, post the question in mind here as a first msg to help with but yes
oh im sorry
I need help with this sum
go read #❓how-to-get-help this channel is occupied
0.75 = 75/100, and can be simplified from there
Ok
in general, it's good to know that certain numbers are divisible by other ones. like any number ending in a 5 or 10 is divisible by 5, like these oens
ohhhh
so that you can divide bot 75 and 100 by 5
15 and 20
yep

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The given conditions are weird, ugh
Yep
what do you have so far
p(p-1/2)<0 so p>2p²
But that doesn't seem to help
As the equality occurs when variables equal 1/3 (i think)
I'm attempting a)
Haven't tried b) yet, because i thought maybe a) leads to b
rz=(1-x-y)(1-p-q), does that help?
Have you tried
- solve for Z in x+y+z=1
and solve for r in p+q+r=1
and plug that into px+qy+rz
yea a leads to b
This?
I'm in grade 10
is this an AM GM question 😭
Probably
It's in the homework section of AM-GM, though some questions also use C-S and stuff
weighted am gm is roughh
Can you not just cheese this by moving the terms arround 😭
How so?
could re arrange it twice
like get
px+qy+rz-x/2-y/2 >= 0
then get by x and y terms
(p-1/2)x+(q-1/2)y+rz >= 0
then we know right p,q,r add up to 1, so we can write that as r=1-p-q
and sub that back into the above equation
(p-1/2)x+(q-1/2)y+(1-p-q)z>= 0 (edit : added the z)
It's rz, not just r btw
yea i am considering z
yea it works
then u would group by x and y
yea but u want p(x-z)+q(y-z)+ z -x/2 - y/2 >= 0
Are you trying to just factor it out?
yea
butt from the assumption that x<y<z
we can say that the coefficients of p and q must be 0 or lower
like (x-z) <= 0
same with (y-z) <= 0
But we're trying to get ≥0
no i mean thats the 2 terms in this equation
We are also given p > 0 and q > 0
p(x - z) <= 0
q(y - z) <= 0
and back to the question you know p,q <=1/2
and since p(x-z) and q(y-z) are both non positive
and we know p and q <= 1/2 we can have a lower bound
p(x - z) >= 1/2 (x-z)
same with q
Wait how?
q(y - z) >= 1/2 (y-z)
which part
This
so basically you know p and q are AT most 1/2
This just means p≥1/2 if x≠z, which is not true in general
No?
multipying by negative switches sign
yeaaa
p(x-z) is least negative when p is smaller and most negative when p is 1/2
Why does this one become y-z?
I'm assuming just a typo
I meant it's q(y-z), not q(x-z)
into this equation
so it would be
p(x-z) + q(y-z) + z - x/2 - y/2 >= 1/2 (x-z) + 1/2 (y-z) + z - x/2 - y/2
yeahhhh
it simplified down to px+qy+rz - x/2 - y/2 >= 0
And i'm assuming for b we try to prove (x+y)/2 ≥ 8xyz?
re arrange x and y and done
Or is b) stronger than a)
LHS ≥x^p. y^q .z^r by W-AM-GM right?
yea this am gm
Wait...
Yeah
proving px+qy+rz>= (x+y)/2 >= 8xyz wont work
part a is under assumption that x<y<z
thats the core logic behind getting coefficients sub 0
Well b) is symmetric so we can assume the order of the variables
At least one set of them
Assuming both sets would lose generality
So we can still WLOG assume x≤y≤z if needed
do idt we need to assume that
I don't even know, there were 30-ish questions, some in the IMO and IMO shortlist but i solved those easier
This question is weird
this is AM GM
what is this triangle man
oh
this is such a dumb way
but what if we say the region of pqr is
v1=<1/2, 1/2, 0>
v2 = <1/2,0,1/2>
v3 = <0,1/2,1/2>
8xyz≤(x+y)(y+z)(z+x)=(1-x)(1-y)(1-z)
Oh hell nah
What in the linear algebra is this
if we prove the inequality works for those 3 corners
it should work for any point inside
so case1 case2 case 3 😭
Can we just use classical inequalities
im joking
there has to be a better way
but this is one way
waitttt
we need to prove the corner case
that (x+y)/2 > 8xyz
given that x+y+z=1
This is equivalent to 9xyz≤(xy+yz+zx) or 1/x + 1/y + 1/z ≥ 9
And x≤y≤z
why 7
no we dont
heres the logic in my head
(x+y)/2 >= 8xy(1-(x+y))
If you don't assume x≤y≤z, we can't have LHS ≥ (x+y)/2
no its the other way (x+y)/2 >= 8xyz
I know, but where are you getting (x+y)/2 from
this is back to v1 btw
You need x≤y≤z to get LHS≥(x+y)/2
x/2 + y/2 + 0z >= 8xyz
testing the corner (1/2 , 1/2, 0)
could chose any corner tbf i just chose that
cus its v1
when i wrote it
u can AM GM that (x+y)/2 >= sqrt(xy)
so x+y >= 2 sqrt(xy)
and then u square both sides
assume idk T as x+y
so it would be T>=2 sqrt(xy)
Hold, i think i got it
T^2 >= 4xy meaning
xy <= T^2/4
yea prove for a corner and by symmetry it works for both the other
No i got it in a different way
how would u do without proving (x+y)^2 >= 4xy
Assume x≤y≤z. We need to prove 1-z≥16xyz, but xy≤(1-z)²/4, so we need 1≥4(1-z)z or (2z-1)²≥0
I did use that
how can you assume x<y<z
Because they have the same role
yea no mb for going into linear alg
idk why but i rlly like using linear alg to abuse symmetry
and just prove one case and be like cus symmetry its the same for other 2 so done
It's okay, i'm doing a research project in spectral graph theory, which involves linear alg so i get what you said
.close
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1
what is the minimum value of the stuff in the parentheses
and at what x does it happen
2+log2 5
not what was asked for
i know,, but i need to find the x at which it happens right
you need to find the x at which the minimum happens, but this x isn't equal to 2+log_2(5)
yeah i know that
i was answering this
if you know that then why give bs answers to mine or @severe verge's questions
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I'm using excel trying to do a loans question.
APR + interest rate
n = amt of times compounded; since this is monthly that would be 12
Y = years (I think)
PMT = the repeating payments (monthlies)
P is supposed to be down payment (Or anything invested initially, if any)
FV =FV(APR/n,n*y,-PMT,-P) That's basically the end result of all of the above put together in a loan plan (in this case I was trying to get to this number through x monthly interest within X years (which I was trying to find for this using goalseek) and with x monthly payments
What I'm not understanding is how I got such vastly different times, I really don't think a $40 monthly difference will amount to ~70yr loan length difference. It couldn't have accidentally translated it into months either because the monthly payment from a previous question for the left set ($50 less) I'm almost positive I got right pays off the loan in 3 years. 72.21 Months amounts to 6.02 years.
Piñata
What is this
@ember river Has your question been resolved?
@ember river Has your question been resolved?
@ember river Has your question been resolved?
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From the usual graph of energy-time it shows for K(t) graph it starts from origin and then reaches max. According to this information option d suites
But (d) not the correct option choice as per answer key
technically all 4 options are wrong since the KE graph should be sinusoidal [check this!]
Yes there isn't charcterstic of sine and consine graph
what's the answer key the book state then
Option c
It has explanation K is max at equilibrium position at t = T/2 and minimum at extreme t = T/4
yes option c is "least wrong"
yeah,but it's still not a sin/cosin function
Because it looks like a cosine?
lmao
not really
cuz this
and also at t=0 KE is at its max
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O)
Why is C greater than A if they are both quaters of a circle
Hi! Just a question but
Hello
Can you explain how the dog gets to these two points?
I.e explain (or draw) how the dog gets to the red point. (And then repeat for the yellow point).
It is because that is the area the dog is allowed to walk in
Well yeah but like
I am interested to see physically how the dog could go to that point
Seeing as the dog is at the point (3, 2) and is attached to a 6m long rope, how does the dog go to the red point?
I know :)
I would have to do sum calculations using the circum
Of all the circles
So...my original question
To do this question, the most important bit is you understand how exactly this dog moves.
In particular,
The only restriction is that the dog starts at the point (3, 2) and can move anywhere that is 6m from that point, right?
Bro wait
(That is not phasing through the wall)
o
My original question was why is c greater than a if they are both quarters
Yep, I know
In general, if two circles or sectors are different, that means the radius of each sector is different.
So the short answer is, the radius of circle C is larger than circle A. That means the area covered by circle C must be larger than the area covered by circle A.
Though, the most important thing to understand is why the radii are different, which was what I was trying to show with my question :)
Okay
Indeed, so how does the dog move to the red point? I.e starting from (3, 2), how do you get to the point marked in red?
Moving 4 units upwards
Uhuh, and?
Opps
Opps?
2 units to the left
Yes
Now, remember that we're trying to find the region that the dog can go to.
The reason why A is then a sector in the first place is because we can imagine that the dog can rotate around the particular axis given by the point (3, 6).
So would it make sense then that, the region of shape A is a sector with radius 2?
What is the difference between it and c?
Good question!
Try and consider getting to the yellow point now :)
Using the exact same logic, how would the dog move to the yellow point?
2 units left and 2 units up
Mmm the thing is,
If you do this, you have only used 4m if the rope
That means the dog can actually go further!
Ohhhh...
My pleasure :)
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Having trouble solving this integral. Supposed to only use the substitution method, this one here was my final attempt and i have no idea what went wrong
oh this one's standard
1/sinx = cscx
multiply and divide by (cscx - cotx)
yeah im a bit of a beginner at this
ahh, bit tricky to think of the multiplication
I see that i tried this before and got stuck with two variables
oh i see what you meant
is there any way to solve it using only the basic trigonometric functions?
this substitution will not help imo
wait
got any hint for which substitution to use please?
you still have some cos(x) remaining
yeah thats why i got stuck on it
you need to express it in terms of t
maybe sinx/2
tan(x/2) is better
yeah that's also commonly used
cos(x), sin(x) and tan(x) are all expressible in terms of tan(x/2) only
and so any rational function with trigs
can be changed into a rational function with regular "x" or "t"
depends on how you call your integration variable
uh?
no
sin(x) = 2tan(x/2)/(1 + tan(x/2)^2) iirc
If you've never seen those formulas, better try to prove them
using the double angle formulas you already know
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thanks for the help
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the denominator isnt telescoping please help
maybe try to find a and b so that
1/(2n-2k+1)(2n-k+1) = a/(2n-2k+1) + b/(2n-k+1)
the numerator also doesn't telescope
maybe it cancels out with the numerator somewhere
what will it do?
that's the problem
what did you get for the denominator
yeah but the thing is i have a thought about it like denominatior could be a bionomial or some standard expansion which cancels with numerator
do it and then you'll see
maybe you can show what you have tried so far
no progress yet i just wrote it in telescoping form
as in, you written the fraction $\frac{k}{(2n-2k+1)(2n-k+1)}$ as a difference of two fractions?
trust me it is telescopic
Element118
no i just gave a thought i didnt know hw to proceed bc it doesn't telescopes
yes
$\frac{1}{(2n-2k+1)}-{1}(2n-k+1)}$
DEXTER MORGAN
$\frac{1}{(2n-2k+1)}-{1}(2n-k+1)}$
```Compilation error:```! Extra }, or forgotten $.
l.49 $\frac{1}{(2n-2k+1)}-{1}(2n-k+1)}
$
I've deleted a group-closing symbol because it seems to be
spurious, as in `$x}$'. But perhaps the } is legitimate and
you forgot something else, as in `\hbox{$x}'. In such cases
the way to recover is to insert both the forgotten and the
deleted material, e.g., by typing `I$}'.
Preview: Tightpage -1310720 -1310720 1310720 1310720
[1{/usr/local/texlive/2023/texmf-var/fonts/map/pdftex/updmap/pdftex.map}{/usr/l```
try splitting into 2 summations and re-indexing the sum
$\frac{1}{(2n-2k+1)}-\frac{1}{(2n-k+1)}$
wdym by re-indexing
"2n-2k+1" might be not very obvious to work with, but you can tell it's an odd number
yeah
for instance say m=2n-k+1, and then write some of the terms as a summation over m
oh i'll let yk if you get smt lmk too
DEXTER MORGAN
i think i have a good idea of the way forwards but i'm just trying to figure out how to explain
how?
don't look for it to telescope
yeah it wont prolly
but try to just write as summations of 1/m
Try using the notation
$\sum_{m\in S}\frac{1}{m}$
where $S\subseteq\mathbb{N}$ is a subset of natural numbers
Element118
you see the two term you have ? if you have to sum them for k=1 to k=n, then part of the terms cancels, the - 1/(2n-k+1) half cancels with the 1/(2n-2k+1)
yes but there is still some expansion which lives
yeah there's a way to deal with that, I think the notation I suggested might be helpful in making it obvious what to do
yes but then you can try to write the expansion in another way for it to simplify with numeratir
that's what I am stuck on
hmmm not sure either
maybe I can step you through on how to use that notation
yeah sure
you have $\sum_{k\in{1,\dots,n}}\left(\frac{1}{2n-2k+1}-\frac{1}{2n-k+1}\right)$
yea
Element118
first it probably helps if you split it up into two sums
i did that
$\sum_{k\in{1,\dots,n}}\frac{1}{2n-2k+1}-\sum_{k\in{1,\dots,n}}\frac{1}{2n-k+1}$
did the same step
Element118
yeah so now we want to re-index - let m = 2n-2k+1 in the first sum, what set of values does m take
try to detail how to change the index on your sum so it's easier
for example if you want to change index of a sum indexed by k=1 to k=n with l = k+n
you know the new sum will start with l = n+1 and end with l = 2n
and then you can make the change in the sum expression
here you want something like l = 1 to l = n in the end
it takes weird fraction values if i express m in terms of n and k
n is fixed in this sum, k varies
so m changes based on k
try plugging in k=1, k=2, and so on until k=n, do you see what values 2n-2k+1 would take?
i'll let you guys know when I'll have some progress on this
what is the bay harbour butcher doing in a math discord server 😭
sorry thats the first thing that crossed into my mind when i saw the username of the person who needed help
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!status
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2. I have begun but got stuck midway.
3. I got an answer but I was told that it's wrong.
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7. None of the above
fn is bounded pointwise, if we had it was defined on a numerable set, then we could get some sub-sequence at least
2
what have you tried so far
let $q$ be a rational number. Can you find a subsequence such $\lim_{k\to\infty}f_{n_k}(q)$ exists?
Element118
this, I got this theorem that says we can get a converging pointwise sub sequence is the sequence of function is bounded and defined on a numerable set E
iirc there's arzela-ascoli, I think the proof can be quite similar
ah, the rationals is a numerable set right, so ${ f_{n_k} (q })$ converges pointwise for every $q \in \mathbb{Q}$
Halex
do you have its proof somewhere, I'd like to see it too but our text book do not include it afaik (Rudin)
yeah you can have that
though now you need to argue that it converges on the irrationals too
which actually... it's not so clear
yes, how do i do 😭
oh wait
it's increasing so there's only countably many jump discontinuities
think about how that can help you select a further subsequence so it converges on the "bad" irrationals
I don't get why at all
each jump discontinuity excludes at least one rational from its image
Every monotone function on $\mathbb{R}$ has at most countably many discontinuities, and all of them are jump discontinuities?
Halex
yeah you should be able to prove it
Let $f$ be monotone increasing, and say $f$ is not continuous at $x$. Consider $\sup{f(t):t<x}$.
Element118
yeah the left limits and right limits exist for monotone functions
Is it the limit to the Left? $$\text{sup} { f(t):t<x } = \lim_{t \to x^-} f(t);$$ if $f$ was continuous at $x$ then we would have $\text{sup} { f(t):t<x } = f(x)$
Halex
we would then have $$\text{inf} { f(t):t>x } \leq f(x) \leq \text{sup} { f(t):t<x }$$ as $f$ is increasing
Halex
But nout sure why its has countably many discontinuities
if the left and right sides are the same, then it cannot be discontinuous
the only way it can be discontinous at x is if the left and right limits are different
but that means there has to be a jump at x
yep, but why can we assume f discontinous at x at first?
you can structure the argument
- say f and x, no assumption whether f is discontinuous
- talk about the left and right limits
- notice left and right limits equal iff f is continuous at x
If they were equal then there would not be a discontinuity, hence it is still countable
from here, you can notice your countably many discontinuities and you can do something to target each of them
if f(a) < f(b), then the possible jump has lenght f(b)-f(a)>0. If there were infinite discontinuities, then the sum would be infinite, which would exceed f(b)-f(a)
did I get it right
consider $f(x)=\left\lfloor\frac{1}{x}\right\rfloor^{-1}$
Element118
of course it's only increasing on $[0, 1]$, but you can easily modify it to have infinitely many jumps
Element118
oh
there are infinite jumps and the sum if finite
yeah which means your argument is wrong
what you need to show is that there are countably many jumps
which includes countably infinite
If $f(a) < f(b)$, the total increase of the function on $[a,b]$ is $f(b)-f(a) > 0$. Each jump consumes a positive part of this total. Therefore, there can be only finitely many jumps larger than any fixed positive number
Halex
okay, then...
Although there may be infinitely many smaller jumps, their total sum cannot exceed $f(b)-f(a)$
Halex
consider the jumps bigger than 1/n
if there were infinite jumps bigger than 1/n, then the total sum of these jumps would exceed the total increase, f(b)-f(a)
so there can only be a finite amount of jumps bigger than 1/n
if we consider the points x such that their jump is bigger than 1/n, n=1,2,...; then the union of these points is an union of finite sets, which is at most countable
<@&268886789983436800> ^
and the union is the union of discontinuities
@regal hamlet Has your question been resolved?
yeah
so there are at most countably infinitely many jumps
now you need to deal with each of them
since that's where all the discontinuities are
think about this
@regal hamlet Has your question been resolved?
yes, we can, by the theorem I mentioned earlier
so can we define $f(x) = \text{sup} { f (q) : q \leq x }$
Halex
only where f is continuos at
@regal hamlet Has your question been resolved?
@regal hamlet Has your question been resolved?
@regal hamlet Has your question been resolved?
not really, you need to use a similar trick
without loss of generality you can choose a subsequence converging at every rational
that's the first step
but then you now have countably many jump discontinuities which you need to handle, and to resolve that, you need to use a similar trick
🤔
Might I have forgotten to mention q is rational?
I'm not sure how to proceed then
look at what the trick on rationals got you - you can guarantee convergence on countably many points
which points are you left where you can't guarantee convergence, and how many are there?
The Irrationals?
[try proving that continuity of f(x) at x implies convergence at x]
@regal hamlet Has your question been resolved?
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,rccw 18th please
exactly in the interior as in we ignore the boundary
But
we can find all points including boundary
and subtract boundary points
do you wanna try? or shd I give some hints?
don't worry, you don't have to count
its simply sum of first 22 natural numbers
-boundary
There is a better and faster way.
Proof?
It is called Pick's theorem.
Expected
Well, I ll ask for written proof
For the theorem?
that still includes half the boundary points tho
doesn't really save calculation no?
Yes
I mean it is the easiest way to solve this; you do need some adjustments.
think abt lines along the triangle, y=0, y=1, y=2 and so on
But making a square seems more appropriate for such problem.
Yes
each line has (22-y) integer points on it
Oh wow
so summing up directly gives you the total points including boundary
Actually man
x+y=42
x=0 has 22 points, y = 0 has 22 points, x+y = 21 has 22 points
but the corners are repeated
so boundary = 22x3 - 3
Oh i see
I think that shd work
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solution for x in R
the final result i got was
cos(pi . e^x - pi/4) = root2/2
Which one are we doing?
well i worked on the cos + sin one
sorry i ended with
2^1/2 . cos(pi . e^x - pi/4) = 1
cos(pi . e^x - pi/4) = 2^1/2 / 2
ill try latex
$sqrt{2}cos(pie^x - frac{pi}{4}) = 1$
Cat 404
Just \ before the sqrt, cos, pi and frac and you good
Also since its a product you can either do \cdot or write nothing
@tranquil pine Has your question been resolved?
i actually solved it thanks a lot
1st and 4th correct
2nd and 3rd are not
bcs when u try em it will give = -1 rather than the correct answer = 1
- k should be R*+
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is this correct?
ye
Would be helpful if you posted what the question was
First derivative?
yes
Or second derivative of it
First
What is happening with the derivative of (x² + 1)²
I found it using the chain rule
(f/g)’ = (f’g - fg’)/g²
But chain rule for this just says (x²)’2(x² + 1)¹
Which is 4x(x² + 1)
Your dv/dx is very wrong
Isn’t that the same picture
Where is the x² + 1
You’ve added an extra x
Second term on the top
At this point I’d say the question is done
You can wiggle the form around but that won’t really change the answer
ik but I've been trying to simplify
There’s not really a point to doing so
Becus I want to
Have you learned about stationary points and how they relate to the derivative?
yh
You could turn this into something - something else
But if you wanted to solve for the critical points of 4x/(x² + 1)²
You want to find when its derivative is 0
Which means leaving the derivative as a quotient is more helpful
Since you can just say look at when the top is 0 (and the bottom not 0)
You could probably factor and cancel one of the x² + 1 terms I suppose
But there’s not much to do beyond that
im trying to figure out how to get it to this form
Factor out a x² + 1
.
You wrote 4x • 4x²
There shouldn’t be a square there