#help-36
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you used $dt/dx = -(1/v^2)(dv/dx)$ right
anflo
i think you have an extra v^2 on the left
@boreal smelt Has your question been resolved?
yea
yea i did a mistake in differentiating
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I would like to fnd the fixed point(s) of $f(x)$. Just want to make sure the way I'm doing it is right.
Let $t \in R$ be a fixed point. Then $f(t)=t$. SO $t= \sqrt[3]{2x^3-x^2-x}$. We thus must solve $x^3=2x^3-x^2-x$ to find the fixed point. Then $x^3-x^2-x=0$ . The fixed points are the roots of this cubic.
waimas
yes the method looks correct
except for the typos
match variables
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\int_{-\infty}^{\infty} e^{-t^2/2} dt = \sqrt{2\pi}
why
$\int_{-\infty}^{\infty} e^{-t^2/2} dt = \sqrt{2\pi}$
Chilll
What have you tried so far?
Use the result of this integral
Oh, your screenshot appears to be from the same page
Gauss hiding behind 1.414
yeah
That's not the same expression, but you can just make a change of variable
After working out the integral, you would need to figure out how you could turn..
yeah but same
$e^{-\frac{t^2}{2}}$ to $e^{-x^2}$
it gives sqrt(2pi)
Erebus
Not much to figure out there
@signal vector gives
@torn heart Has your question been resolved?
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Let circle (O) have diameter AB = 2R, and chord CD be perpendicular to OA at the midpoint M of OA. The tangent at C of (O) intersects OA at N. Draw a circle with center D and radius DM intersecting (O) at E and F. Draw diameter DP of (O), DP intersects BC at I and EF at H. Let K be the intersection of EF and CD. Calculate DK in terms of R.
any progress?
i read through your proof and ill just ask a question: How did you get $DM = \frac{R\sqrt{3}}{2}$?
1 divided by 0 equals Infinity
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thêm 1 ng việt trên đây 🙂
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how do u solve part b
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Might be a strange question, but why does observing that we have drawn a white ball increase the probability that the ball that was transferred was white? I get that if we do the math with conditionals, we see that there is a dependence, but I don't really get intuitively how it "affects" the outcome. There's nothing saying that x% of the time, a white ball is drawn, which would tell us something substantial, but in my mind this is a single observation telling us a lot.
the bayes part of this really screws it up
what Im thinking is theres ways to explain the bayes formula or to make it plain obvious in other examples
maybe you look up a few videos, then try and use their words on this problem
Im just thinking if the ball was black, theres no way transferring a white ball is going to help the odds
or maybe you could draw a tree diagram for it idk
but if the ball is white...
I can visualise the tree diagram and I (hope) understand Baye's formula, but I can't seem to accept that simply observing something once "increases" the odds
...why is my drawing program drawing different thicknesses for differenc olors
there would be flying cars in 2025 they said
I'm not really sure if I'm getting my question across well
this is basically how I solved the question
but something that bothers me is that observing something afterwards "affects" the probability in retrospect
if that makes sense
oh thats all?
if it didnt, itd be 50%
if it did, itd not be 50%
thats it
you can see theres more white balls available in one of the options
so when you choose a white ball, its more likely its the top one
and so its more likely that a white ball was transferred than a black ball
indirectly because a black ball leads to fewer of the outcomes
and also indirectly because a white ball leads to more likely outcomes than a black ball
at the point of transferring, shouldn't P(transferred ball is white) be 2/3, since whether a white or black ball is observed in the future doesn't affect the present?
thats not true
if you throw a box off a cliff then you find out there wasnt a cat in the box at the time of throwing, that tells you there wasnt a cat when it was thrown off the cliff
that's shrodinger's cat experiment (the two dots above the o fell off the cliff which is the reason for the variant youre reading rn)
similarly you just found out the ball is white
youre saying that tells you nothing about the state of transferring the ball?
so in some sense, it's correct to say that the future affects the present?
inuka use that common sense
the present lets us know about the past
thats called history
you did history pulling a white ball and then thinking about what mustve happened to let that happen
if youre pulling balls out, thats not the future either, thats the present
you can also just shift all the verbs to be future and present instead of present and past
same argument works there too
in my mind, even this doesn't feel true when it's just one observation
..as opposed to how many observations?
that's interesting yeah
any observeration is usable information
if we took 10 observations with replacement then it seems like it tells us something
but then if you just reduce the amount
surely 1 tells you something
that's very strange to me
then what was even the point here
we cant get much out of 1 ball
but its bold to say you get nothing
not even a little bit of information? we saw the ball
ok that's fair
you can split up the cases like this
since we're factoring that information into our calculation, surely that means we can quantify how much information a single observation gives us
oh thats not good in dark mode
I dont know entropy so Im not answering that
as for this,
if upon seeing a white ball you guess that a white transfer mustve happened, you have a 4/5 chance of getting it right
this is because in two of the three scenarios, you were given more white balls to infer such
a white transfer directly boosts the chances to have picked a white ball
and so the chance changes, and moreover gets higher
oh interesting, so it's something like the sub-state-space that we select from is larger
if on the other hand any white transfers never ended up in the second urn,
history is repeating itself, put that background back
you can see youd still have the usual 2/3 chances
in all of the scenarios, the white balls in the 2nd urn are the same before and after, so you gain no useful information had you pulled out a white ball
ok that's kinda interesting, I'll play around with this for a bit
thanks for the help
np
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H and P_A are the orthocenter and A-Humpty point of ∆ABC then H,P_A,B,C are concyclic. Why?
what definition of humpty do u use
(or what equivalent facts do you know about it)
∠P_AAB=∠P_ABC, ∠P_AAC=∠P_ACB
It's the intersections of circles that go through A and touch BC at B,C
I know the definition of that
Through some weird (kinda famous) proof of Ptolemy's theorem
But i'll prefer not to use it
hmm ok well yeah actually we don't need that
lol
because you can just angle chase
Do you know <BHC in terms of the angles of triangle ABC?
∠BHC = 180°- ∠HBC - ∠HCB=180°-(90°- ∠B)-(90°- ∠C) = ∠B + ∠C
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lol yw
the reason I mentioned inversion was because a lot of properties about the humpty (and Dumpty) point are very easy to prove with inversion
its not needed in this one but it makes other properties much easier to prove
so when you learn inversion you can try to come back to this config and prove other properties with it
Thanks
Today is the first day i learn about those points though, i guess i'll stick to the basics
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"Hi everyone! I'm from the Philippines and I'm aiming to win the Division Math Celebration Quiz Bee for senior high school. I'm in Grade 11. I think the competition will focus on statistics what i would do
What do you need help with
you got any revision or smth like that?
@lunar cairn Has your question been resolved?
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Not yet
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Ya I am pretty sure this problem is nonsense
Cuz AEC is essentially AEB
currently trynna see this problem assuming BE is not a straight line
(But yea assumign that how would I know which one is straight and which one is curved
are you this sure this is true?
Hmmm what do you want me to do find solid angle?
I see typo
yeah I dont think any of the lines are curved here
it's just this
Let's try for ACB and check if any option matches, ig.
Now what does that mean
Angle ACB
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How to find this limit ?
I know that the product of the dominant terms on both nominator and denominator[(2n^3)(3n^5)/(2n^6)(3n^2)] will decide the result .
Well as n tends to inf, the +1 and -1 will become insignificatn so how else can u write the limit?
yep
careful with ()
How do I factor out the (2n) if there is an exponent, lets say top left
i think factoring just n will do the trick
if I had like (2n-1) I would just "do" n(2-1/n), but how do I "get it out" when there's the exponent?
(2n-1)^3=(n(2-1/n))^3
$\left(2n-1\right)^{3}\ =\ n^{3}\left(2-\frac{1}{n}\right)^{3}$
oh, i jst keep it like that 
Xerxes
I see. thanks
its the same thing if we take n common from all the terms
I see.
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I don't really get this
The justification that is
The value of the parameter that maximises the joint dit
so the value that maximizes L(theta)
L(theta) only has two values, 0 and (1/2)^n
since (1/2)^n is the max
any value of theta that gives you L(theta) = 1/2^n is an MLE
Also, @scarlet sequoia before the channel shut in our faces, you mentioned including an indicator function, but wouldn't that change nothing since the indicator function is the same every time?
I didn't mean to close the channel rudly last time , sorry
the indicator function is {2theta <= x_i <= 3theta}
so intersection is {2theta <= min(x_i) <= max(x_i) <= 3theta}
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In an equilateral triangle ([ABC]) with side length (\ell), the value of ((\vec{AB} + \vec{AC}) \cdot \vec{BC}) is:
(A) (\ell^2)
(B) (\sqrt{3},\ell^2)
(C) (\dfrac{\sqrt{3}}{2},\ell^2)
(D) 0The exercise does not include any image. I was looking at the solution, but I don’t understand why (\cos 60^\circ) and (\cos 120^\circ) appear, and why we are multiplying by them.
for vectors in general,
u • v = |u| * |v| * cos(theta)
where theta is the angle between u and v
@blazing kindle
i know we use cos but why 120 degrees and 60? in the exercise just saying equilateral triangle dont show any imagem or saying addictional info
in an equilateral triangle the interior angles are always each 60°
the angle between vectors AB and BC is 180 minus that
oh
i see
tysm
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prove that r is irrational if r^3 + r + 1 = 0
Sean [Ping On Reply Please!]
step 1: solve the cubic
what now

i am a nub idk if that was sarcasm
anyways $\frac{p^3}{q^3} + \frac{p}{q} + 1 = 0$ right?
1 divided by 0 equals Infinity
p^3/q^3 + p/q + 1 = 0. how can you make this eq less scary
yeah
put back r = p/q
congrats, you're back to square 1
why 1 on rhs
don't put spaces between $
also you shouldnt have put a space after the first dollar
Sean [Ping On Reply Please!]
you could have used q^3 as your denom
having the denominator is scary
p^3 + pq^2 + q^3 = 0
$p^3 + pq^2 + q^3 = 0$
Sean [Ping On Reply Please!]
now do i have to solve this
for strongness
idk what to call that
$p \in \mathbb Z$, $q \in \mathbb N$, $(p, q) = 1$
1 divided by 0 equals Infinity
you don't have to "solve" this per se
then do i have to prove that this is never 0
also yes it will be good to start off with r=p/q in simplest form
which is this btw
is that the gcd (p,q) ?
this eq rearranges to q^3 = p(-p^2 - q^2)
yea
$q^3 = p(-p^2 - q^2)$
Sean [Ping On Reply Please!]
🔥
contradiction?
1 divided by 0 equals Infinity
then what
but if you substitute back $p = q = 1$ then that does not satisfy the equation
1 divided by 0 equals Infinity
$p = -1$, $q = 1$ also satisfies this, but try to plug back into the original equation
this equation?
1 divided by 0 equals Infinity
like literally your question
so are we done
yeah that completes the proof
so if (p,q) = 1 then p not | q?
and except p = -1, q = 1
and except p = 1, q = -1
then it's true for all the remaining cases

can we do this by breaking into cases
cases such as p is even and q is odd
and p is odd q is even
then both odd, etc
yea
apart from $\abs{p} = \abs{q} = 1$
1 divided by 0 equals Infinity
then this statement is true
so that's why we gotta consider the cases of $p$ and $q$ being $1$ or $-1$
1 divided by 0 equals Infinity
which i believe if you try to substitute in your $r^3 + r + 1 = 0$ then it does not satisfy
1 divided by 0 equals Infinity
You've essentially assumed that p/q is your answer, already simplified
Towards the end of the algebra stuff you've concluded that p and q are from {1, -1}
But then that makes your answer either 1 or minus 1; but you can easily check that these are not solutions
,w solve r^3 + r + 1 = 0
proof done 
give me another proof question like this
ooh
prove that sqrt(2) is irrational
nah that's too simple
what
thats the first prove they teach in a discrete math class
Prove that $\forall k \in \mathbb N$ that is not a square number then $\sqrt{k}$ is always irrational
1 divided by 0 equals Infinity
how about now
(idk how to do it)
ok ig i can try
i will use contraposition
$\sqrt2$ too simple
1 divided by 0 equals Infinity
contradiction you mean?
no contraposition
ahhhhhhhhh
I mean in the sense that this is the same type of question
Assume the opposite i.e. that your answer is rational; arrive at a contradiction
root k is always rational for all k belong to N that are squares
Starting with that, and then showing sqrt(p) is irrational for any p prime, is good practice
if root k is rational then k is a square
hm
root k = p/q
so you arrived at a contradiction that fast
k = p^2 / q^2
k = (p/q)^2
so $k = p^2$
1 divided by 0 equals Infinity
aight i see
is this valid
wat
that's too fast 
is my proof valid?
yeah enough of the roots
proof by contraposition
No, because of this line
"k is a square" is shorthand for "k is the square of some INTEGER"
But all you've said is that "k is the square of some RATIONAL p/q"
You've not shown that q must be 1
It is also, crucially, NOT a contraposition
there is a rather nifty argument using parity
that's why the $\gcd(p, q) = 1$ assumption is so important
1 divided by 0 equals Infinity
but I would rather not spring that on OP atm
it's called ||contradiction||
Contraposition is when you attempt to prove
[ Statement A is true ] implies [ Statement B is true ]
by demonstrating that
[ Statement B is false ] implies [ Statement A is false ]
how is it called contradiction, i took the contrapositive of the original conditional
then i proved the contrapositive
Contradiction is when you want to prove the opposite is wrong
i proved that the contrapositive is true
Because that's not what contrapositive is.
Contradiction is that you prove from what you have to prove statement B is impossible to happen
what you did here is contradiction
the question:
is k belong to N is not a square then root k is irrational
contrapositive:
if root k is rational then k is a square
but k is not a square
it's a contradiction
ContraDICTION is a type of contrapositive which goes as follows:
[ the universe makes sense ] implies that [ A is true ]
Taking the contrapositive of THIS is what contradiction is:
[ A is false ] implies [ there is something wrong in the universe ]
so k is a square
If root k is rational... Okay, now you have to show that this fraction is over ONE
You HAVE NOT done that yet.
what is over one
you did not show that p/q is an integer.
$\frac{A}{1}$
1 divided by 0 equals Infinity
p and q are ints, p/q is not
yes
(p,q) = 1
if p/q is not an integer, then how can k be a perfect square?
p/q is only a rational number
Yes, but p OVER q IS NOT AN INTEGER, IT IS A FRACTION.
ragebait ahhhhh
am I using non-standard terminology or sth wtf
i think you got ragebaited
the whole idea of the proof is that if k is a perfect square, it should be the square of some integer
not a rational
im jus slow sorry
unless the rational happens to be an integer, but not the case here.
at least you've not shown that to be the case
ill have an easier question for you
Yeah, so, you CAN solve this by proving
root(k) is rational => k is a square (of an integer)
but this isn't done
prove that an irrational number + a rational number always results to an irrational number
how can k be a square
Start with THIS one first
its a fraction
You need practice at figuring out what it means to say something is rational or not
the contrapositive method is really not the best method to attack that particular problem.
So start with 1/0=inf's question
it is very hard to show that q = 1.
ok i assume that rational + irrational is rational
then i give a counter example of root 2 and 1
||why does everyone call me that lol||
||i go by Infinity||
i am disproving a statement using counter example
ok i assume that rational + irrational is rational
i am disproving my assumption
Okay, even if you tried that (and this doesn't really work here, because you're trying to prove this FOR ALL config.s); how do you KNOW that root(2) + 1 is irrational?
oh
right
Sean, have you learnt about quantifiers?
Nah, this could work tho actually; he's disproving the negative of the desired statement, so...
yea
how do i express an irrational number?
be aware of the quantifiers of the statement you want to prove.
rational i can do with p/q
Those aren't quantifiers...
You are showing any rational x, any irrational y, x+y is irrational. If you want to disprove that, logically you can try to find a rational x and a irrational y such that x+y is rational (though it will be impossible) and you didn’t achieve that
you can only use an arbitrary counterexample if your quantifier is $\exists$, not $\forall$. $\forall$ requires a stronger argument.
Lute
alright im stuck
well, since one of them is rational
where to go from a + b = p/q
assume $a$ is rational
1 divided by 0 equals Infinity
Contradiction because...?
may I know if you're doing discrete math, number theory, analysis, or something else?
i assumed that b is irrational
discrete mathematics freshman year CS class
This reads like you're assuming a is irrational, not b
i assume a is rational and b is irrational
so what about b lets you express it as m/n? what is m and n? you'll have to state them clearly in your proof.
At least you are warmer now.
You can assume there exists rational x, and irrational y, such that x+y is rational, then … … contradiction.
What you did originally was you assumed x=1 and y=sqrt(2), which doesn’t make sense
i miss the xmas icons
a + b = p/q
r/s + b = p/q
b = p/q - r/s
I can't prove to you that I've bought apples without showing you the apples I've brought
now what
take the lcm or smth
Show that p/q - r/s is rational
b - ps - rq)/rs
ps-rq is an integer
rs is also integer
rs != 0
so it is rational
also, since 1/0=inf's question is no longer in contention, if you'd like, I'll show you an example proof for his statement of sqrt(k) being irrational iff k is not a perfect square.
i think i mentioned what do i go by in this channel...
sure
this does require you to recall what prime factorizations are and what a perfect square means in terms of its prime factorization.
what is $v_p$ here 😭
1 divided by 0 equals Infinity
no need
p-adic valuation
$nb^2 = a^2$, this means that $b^2 \mid a^2$
1 divided by 0 equals Infinity
and $\gcd(a, b) = 1$
1 divided by 0 equals Infinity
contradiction
not a contradiction yet
I did not say it was the most efficient.
|a| and |b| = 1
yep
it was meant to be an example to get OP to see the kind of structure that is expected of a proof.
so where do i plug the a and b now
anywys
ah i see
And it surely is a marvellous one (unfortunately [margin joke here])
but if you insist on it, I'll remove the proof, and I apologize for sending a complicated proof here.
anyways, this is just an example on how you can write your proof @torn dome
no need to remove
oh mb im too late
in discrete math, or are you ok with other fields?
basic math
sure, let me get one from my stash
how many proofs have you written @bold turtle
do you also write formal proofs (like not just for the sake of solving a homework question, but for something of real value)
"For something of real value" requires even MORE vigour, you know
The whole point of homework questions is SO THAT you learn how to write these in presentable manners in the first place
Prove that the square of a positive odd integer leaves a remainder of 1 when divided by 4.
(alternatively: prove that the square of any positive odd integer is always 1 mod 4.)
Also, I'm not sure this is answerable; I've completed a maths degree, so it's probably in the hundreds, if not thousands
hint: use the algebraic definition of an odd number.
are you a maths major
your role says undergrad
CS master's degree student; I've done a maths undergraduate degree
(I'm not American, so "major" is meaningless here)
who just pinged me in #graduate-applications 😠
Back to the question at hand... ^ @torn dome
and in #math-pedagogy too 😭?
!redir, please.
This channel is only for on-topic discussion. Please take casual conversation to #discussion or #chill.
i assumed any arbitrary n odd number = 2k+1 then i took the square
n^2 = 4k^2 + 4k +1
then i used long division
i am getting remainder = 1
ok not too bad of an attempt, and I presume you did your long div correctly
yeah
but from 4k^2 + 4k + 1, you could have factored out a 4k from the first two terms to get 4k(k + 1) + 1
-# yh, tbh, I'm intrigued on what you did that you're calling long division
from here it's more directly obvious that you will have a remainder of 1 on division with 4, because k integer means k+1 integer, and 4k is obviously an integer multiple of 4
so (integer multiple of 4) times (integer) = (another integer multiple of 4), and + 1 makes the remainder 1
,rcw
which is better
I'd prefer the factoring method because it leaves the dangling + 1 as undeniable proof
are you saying that i should write $n^2$ as $4k(k+1)+1$
Sean [Ping On Reply Please!]
yes.
how can i show that there will be remainder of 1
^
bruh, the literal dangling 1 outside of that bracket IS the remainder
^
consider that k is an integer. that means k+1 is an integer too.
yeah
then obviously 4k is also an integer.
yuh
more importantly, 4k is a multiple of 4.
and multiplying anything by a multiple of 4 makes the product a multiple of 4 too
so 4k(k + 1) is a multiple of 4
- 1 gives the remainder
end of story
cf. how if you write 194 = 14 x 13 + 12, then 12 is the remainder you get when you divide 194 by 13
well i could have done $4(k^2+k)$
Sean [Ping On Reply Please!]
Yh you can, and that's equally valid
The point being, you can clearly pull out a 4, and get a remainder of 1
a distinction without a difference
k^2 is clearly an integer from k being an integer
the sum of two integers is an integer, and multiplying by 4 gives a multiple of 4
- 1 still gives the remainder
end of story
^
cool
I never said it was wrong.
but polylong div is prone to rather dumb errors from time to time
and thus I opt to not do it if I have better ways to show what I want to show
I'll leave you with one final question
take your time in doing this
given p, q are positive integers. show that p/q + q/p >= 2 always.
note: consider using contradiction.
That's pretty tame compared to the full AM GM tho wdym
In fact you're technically proving the AM-GM here for two numbers
yeah
i arrived at p < q
or more insightful
is that wrong
ok so for one thing right
idk how you get that
when doing proofs and wanting to get your answer checked
assumption?
it might help to show the whole proof
because arriving at a right conclusion from illogical steps renders the proof moot
for instance
"I have 3 apples because the spaceship man landed on the moon, and therefore I have 3 apples" is not a valid proof
sqrt(2) is irrational.
assume sqrt(2) is rational if I can be on this server.
I can be on this server, so sqrt(2) is rational (wtf?)
when writing proofs, the reasoning is as important as the conclusion
indian mathematics questions solved here?
idk
you can ask for help in an available channel. please read #❓how-to-get-help
!occupied - jeez does no one read the damn info file
Someone else is already using this help channel. If you need help with a question, please open your own help channel/thread (see #❓how-to-get-help for instructions).
ok well if p/q + q/p < 2
then p^2 + q^2 / pq < 2
p^2 + q^2 - 2pq < 2
(p-q)^2 < 0
p-q< 0
p< q
check his bio btw 😭
-# They're asked, and seldom solved (because of the type of question and the nature of the answers sought 😭)
your proof is correct up till you made two extraneous steps
p-q< 0
p< q
these two
p < q and q < p
-# scam likely 😭
(p-q)^2 < 0
you should have stopped here
this is the contradiction you're looking for
Because that should've sent alarm bells ringing
these 2 steps don't make sense
i didnt use parenthesis
also I suppose you meant < 0 on the second line there
yh you're gonna wanna write them in esp. if you're typing these out
alarm bells should be ringing - why?
what do you recall about squaring real numbers?
ok
got it
square is positive
ok so proved
or...?
0
ye
yay
Try and write up a proof
exactly.
ik how to write proofs trust me guys
...
i did one in my MSE
I'm currently mashing the X-to-doubt button fwiw
i got 2/5
yo @torn dome
since you learned your technique
why don't you go and try to help #help-2
that does not scream confidence, but if you do not want to have your proof writing reviewed, then sure, I won't force you to
their question is to prove $\sqrt{3}$ is irrational
1 divided by 0 equals Infinity
i solved that one already
ok i will send it here
try and help him
It's beneficial to see if you've actually learnt it well if you can teach it to someone too
by yourself
i dont help, i am helpee
.
i agree
but i have the discrete mathematics final tmr
if you help him, you are actually trying to revise the stuffs you learned by yourself
just come and try to help
ill backup
to be fair, let him settle his finals first
plus, this is kinda advertising other help channels alrd
btw, I forgot to explain why your last two steps were invalid
from (p-q)^2 < 0, we know that no real number satisfies this inequality
therefore, taking a square root leads to complex numbers being introduced
and complex numbers are, well, not exactly well-ordered, or even ordered at all...
so the notion of p < q or q < p breaks
@gleaming anchor
well written
took you 10s
it's not hard to read font 24 writing
plus, I already caught the gist of your algebra
I just wanted to see your sentences
thank you Celine!
rip the accent but nps
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how are there 2^k terms (in last step)
wait who r u claiming is a troll
@warm junco don't troll. It distracts people from getting help.
@torn dome does this answer ur question
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what is the best method of proof for this
direct proof doesnt work, i get stuck at 4k^2 + 4k
Can you factor 4k^2 + 4k
4k(k+1)
yes
We want it to be divisible by 8, so since it has a factor of 4, what are we missing?
2
Indeed, to show k(k+1) is divisibe by 2 it is possible!
an integer
With reference to division by 2 then, k, as an integer must be either _ or _
Right, so in either case, k(k+1) has an _ factor
2
Exactly!, so k(k+1) is always divisible by 2
what to write in the proof
i am proving for 8
you're left with 4 k (k + 1)
yeah
and you can say that for any k
k(k+1) is divisible by 2 and 4 is divisible by 4, so the whole thing _
either k is even
meaning there is a factor of 2
or k + 1 is even
which also means there is a factor of 2
so that means that you can write 4 k (k + 1) as 4 * 2 * l
how about we use induction on this
l being another integer
btw how can i prove that k(k+1) is always even
You basically did before
i could make two cases
You just proved it
like when k is even and when k is odd
then i can multiply
okay
btw what abt induction
You don't need induction because for all the steps you've gone through you haven't said anything about n or k
Seems overkill when you can prove directly but it does work very nicely
One of the easier inductions to write out
i used to do these typa problems using induction
is this one also possible using direct proof or some other method
$11^{n+1} + (11 + 1)^{2n - 1} = 11^{n+1} + 11^{2n - 1} + 11^{2n - 2} + \dots + 11 + 1$ and $11^2 + 11 + 1 = 133$ so it should be possible to prove directly
Coolempire2026
Likely easier by induction though
how did you expand that power
Binomial theorem
i will write my so far progres, you tell me how to prceed
holon
So after the base case and inductive step process I reached at $11^{k+2}+12^{2n+1}$ with the assumption that $133 | 11^{k+1}+12^{2k-1}$
shiite
anyway can you help me with the next step
how do i proceed
So what is your base case?
Sean [Ping On Reply Please!]
n = 1
yeah
of course it works, thats why they gave a whole question on it
so i am straight at n = k + 1
right so you assume it works for k
yeah
so now you go look at $11^{k + 2} + 12^{2(k + 1) - 1}$
Katharine
You wanna transform this into some shape such that you can use your assumption
$11^{k+2}+12^{2k+1}$
Sean [Ping On Reply Please!]
how to use this
to 'transform'
ik that i gotta add and subtract smth
should i do $11.11^{k+1}+12.12^{2k-1}$
what you can do is use the binomial theorem
Sean [Ping On Reply Please!]
Are you sure about the 12
Check the exponents
(When you take out 1 twelve, the power should decrease by 1)
Sean [Ping On Reply Please!]
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The way I solved it is in #latex-testing for comparison
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Guys, for context, I am still new at math, and I've been learning all the basics, so I'm not good at it, and I am the type of person that can't move on without understanding the why's to everything, my question is:
how do we know that [ACD] is similar to [DBC] ?
I see the square angle at D, and I understand it is a similar triangle but why? sorry if my questions are too basic, I'm going step by step
they're both right triangles that share a length
I think that sufficies similiarty.
oh so you only need to share the length and them both being right triangles? :O
🤔 no you need one other angle to show it as well, otherwise a bunch of triangles are similar
(Which is easily shown since the big triangle is similar to them both)
oh okay, because I was trying to prove it with AA - Angle angle, or maybe SAS - Side angle side but I'm not being able to
apologies
oh and this exercise is from khan academy
Yeah AAA is how I did it when I looked as well
ACD is similar to ABC because they share angle A and the right angle (angle C/D)
ABC is similar to CBD because they share angle B and the right angle (angle C/D)
ACD is similar to CBD because they are both similar to ABC
One question, sorry, how do I know that both angle [ACD] and [ABC] are the same? I'm a bit confused there, sorry
you dont need to apologize by the way! nor are your questions "basic". we've all been there we've all done that and It's really cool how you're willing to understand instead of memorizing!
Thank you a lot for your* comment! c:
also for this, notice how ACD is 90-BCD. and guess what! DBC is also 90-BCD.
omg you are right! :O
hi 
ohhhhhh I see what you mean, based on that you can conclude that no only is angle C = to angle B, but that also angle A equals Angle C (on BCD)
first conclusion is from angle ACB as aw hole being acute, and thus, angles BCD and ACD must sum up to 90. BCD + ACD = 90 and thus ACD= 90 - BCD
second conclusion is from the right triangle DBC! sum of all angles in any triangle is 180. you already know BDC is 90 and thus 90 + DBC + DCB = 180 and thus DBC + DCB = 90 and thus DBC = 90 - DCB
makes a lot of sense, I think like I can understand and prove similarities based on angles a lot better now
of course! keep practicing.
because I can solve this exercise which is to just calculate the area of the triangle, but I always stop whenever I see something I don't 100% understand or can prove ,-,
thank you, how do I mark this as solved?
you type .close
always!! I wanna go to mathematics in University
.close
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AMAZING!
BEST OF LUCK
YOU CAN DEF DO THIS!!!
maybe someday I will be able to help people out here too
yes! you should start helping postgrads like @hasty mist because they dont know their maths.
so you want me to be completely demolished I see ahah, I will resume my studies now, thanks and thanks coolempire too! c:
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I have been doing more math exercises about this topic, I will do a few more and move on, but I did a visual representation of why they are similar with the AA criteria with this drawing, this sometimes helps me understand concepts, trying to formulate them myself, just wanted to put it here, if there's anything I'm missing please tell me! Thanks a lot everyone!
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because the outside part of the shape has a higher rotational distance than the cone part
the part with a large area of the cone moves less distance than the large area of the cylinder
can you put it into simple words i dont get it
well just look at the 2d image you posted
the ratio between the areas is 1/2 right
half
yea
now if we rotate it along the line, you see how the inside becomes a cone
and the outisde becomes a cylinder, without the cone?
well as the triangle part is closer to the center, it will gain less volume. While the outside part, as it is further away from the center, will gain omre volume.
Try to visualize this
what i was thinking
is that the ratio would stay consistent
in every rotation frame
so when the 3d shapes are form how does the overall ratio change
ohhh
i get it
overlap
ohh
is overlap right reasoning?
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incomes are 2x and 3x, expenses are 16y and 21y, savings are 4z and 9z, and 4z+9z = 312000/12
also savings is income minus expenses 😊
Nevermind
The answer is Rs 60000 per month
!nosols
As a helper, please do not give out answers that could be copied as a homework solution. Have the student work through the problem themselves and guide them along the way.
this op already said
What?
You're not helping someone to understand if you just tell them the answer
fixed a typo btw
Oh got it
312K is the annual savings of the two people combined
Ok btw I solved it in my notebook
ok sure. good for you.
let's wait for OP to show signs of life again so he can tell us if he's stuck or if he also got it
@restive sinew you here?
I think he's gone
@restive sinew Has your question been resolved?
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How do I start it?
If the speed of $A$ is increased by 14 km/h, he will be 4.2 minutes early and if the speed is decreased by 2 km/h, then he will be 0.8 minutes late
1 divided by 0 equals Infinity
i think this requires a system of equation
let the time $A$ makes through the distance as $x$ and the speed $A$'s going is $y$
1 divided by 0 equals Infinity
so the distance we need to find is $xy$
1 divided by 0 equals Infinity
.
generally speaking, a good first idea is always to give names to all values
and then try to find some equations connecting them
@restive sinew Has your question been resolved?
@restive sinew
@restive sinew Has your question been resolved?
@restive sinew Has your question been resolved?
op is not showing any signs of life
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AB: 3y-2x-5 = 0
AB distance = sqrt(13)
i took a point P (x,y)
distance of P from line. =
d=|2x1-3y1+5|/sqrt(13)
area = 1/2 x (2x1-3y1+5)/sqrt(13) x sqrt(13) = 10
2x1-3y1+5 =20
2x1-3y1 = 15
a=2 b=-3
which gives me ans 4
which is in the options but is wrong
where did i go wrong
What the hell is that font size
sorry its from some website
I guess here
Forgot the modulus
Also u gotta use the fact tht P is above line AB
so like 3y-2x-5>0?
If P is above the line then putting it into the line's equation will be positive
It could be below too right? Its locus
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Mentioned in ques
question specifies above

.