#help-10
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yes
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I don't understand this step
the given proposition is that $\frac{a}{b} = \frac{c}{d}$
Mushaar
Hi
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For a given (false) claim and proof, what skills do you use to determine where the proof is false?
Pretty vague to give anything meaningful. Generally counterexamples or proof by contradiction
I have a specific proof that I know is incorrect but I’m having a hard time to figure out which step exactly the proof is wrong
@tardy epoch
don't ask to ask

Oh I sent the question idk where it went
And A’ = A is complement and A\B = A - B @timid silo
yea counterexample would be fine here
But what step from the proof would be wrong?
I was thinking step 10
counterexample would be easier
Yes I know but I’m just trying to figure out where the proof is wrong
And then I can proceed to this
@proper snow Has your question been resolved?
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So why does “squaring the circle” exist
Basically my second question on #1154481698411642890
what answer are you looking for exactly
Why is a circle bigger than a square that it fits in
🙄
What about the answer
.
.
that's different from squaring the circle
I might saying it wrong too
again, not answering my question
Whats it
from this, what do you want ?
what kind of answer
Like proof
I cant rn
then work on it when you can
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Is this solvable for f(x)?
Best I can get is this, but still cant integrate the left side from what I understand
If it's not solvable, is there another way to find the parametrization for x^2 where the velocity is constant?
Yea they give a function x in terms of y. Looks nearly impossible to invert
darnit
,w f'(x)sqrt(1-4f(x))=1
W|A inverts it pretty well
but I wouldn't solve what the separable gives algebraically
Mrfancy is a wolfie whisperer
,w f'(x)sqrt(1+4f(x))=1
oh damn I did 
Well I'll be damned
,w f'(x)sqrt(1-4f(x)^2)=1
therree it is
ok, cool
yeah that looks nasty
yeah im not sure if the inverse works for what im doing, but I can try lol
it's also only between -1/2 and 1/2 😭
maybe the way I went about trying to find this was complicated, so I guess ill just explain the whole problem:
I wanna parametrize the equation y=x^2
but with a constant speed
And that's where that equation came from lol
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I'm working through Shankar's textbook and am confused on how to proceed with this classical mechanics question (Ex. 2.7.8, (2)). We have been given an arbitrary point/coordinate transformation $$ q_i \rightarrow \bar{q}_i(q_1,..., q_n)$$ and we have already derived the equation $$ \bar{q}_i=\sum_j \frac{\partial q_i}{\partial\bar{q}_j}\dot{q_j}.$$ We want to show that $$ \left( \frac{\partial \dot{q}_i}{\partial{\dot{\bar{q}}}j} \right){\bar{q}} = \frac{\partial q_i}{\partial \bar{q}_j}.$$
So far I have that $$ \left( \frac{\partial \dot{q}_i}{\partial{\dot{\bar{q}}}j} \right){\bar{q}}= \left( \frac{\partial}{\partial \dot{\bar{q}}_j}\left[\sum_k \frac{\partial q_i}{\partial\bar{q}_k}\dot{qk} \right]\right){\bar{q}} $$ $$=\left( \sum_k \left[\frac{\partial q_i}{\partial\bar{q}_k}\frac{\partial \dot{\bar{q}}_k}{\partial \dot{\bar{q}}_j} + \dot{\bar{q}}_k \frac{\partial}{\partial{\dot{\bar{q}}_j}} \left( \frac{\partial q_i}{\partial\bar{q}k} \right)\right]\right){\bar{q}} $$ where I simply applied the product rule.
I am confused on how to continue, since isn't it possible that $\frac{\partial q_i}{\partial\bar{q}_k}$ can be a function of both $\bar{q}_j$ and $\dot{\bar{q}}_j$? Also, can someone please explain why it's important that we take the partial derivative with $\bar{q}$ held constant? Isn't holding $\bar{q}$ constant already implied by the partial derivative?
thedude365
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this one asks to find the angle between 2 lines in R3
I did the dot product over the 2 magnitudes
aka this, which gives the angle
however it states im doing this wrong
i did -17/(sqrt(18)*sqrt(29))
giving me an angle of 138.0792
in the end
(this is all in degrees)
@formal inlet Has your question been resolved?
<@&286206848099549185>
okay one moment
Take ur time
ok sorry for the hold up
i worked it through and ended -26/sqrt(89)*sqrt(61)
ok lets work it out together again
from the beginning
we have two vectors
d1 = (-3,4,-3) + t(-1,4,-1)
and d2 = (0,0,-4) + s(3,-4,-2)
and cosx = d1•d2/(||d1|| ||d2||)
@formal inlet are you with me
yes
ok now lets pick any values for s and t
yeah ive had all this info is right so far
good
since it'll lie on the same line regardless
what do you pick?
does it have to be 3 values each xyz?
no t and s will just be a number
then we could just do 0,0,-4 and 3,-4,-2 as tghey are both on the lines right
3, -4, -6
d1 = (-3,4,-3) + (-1,4,-1) and this too
ok so d2 = (3, -4, -6)
-4, 8, -4
and d1= (-4, 8, -4)
ahhh so I use these for the equation instead?
now lets plugin and see what we get
correct
lemme do the same

d1
nvm
let me verify
-20
sqrt(96)
and d2
and d2 sqrt(61)
i got all of those too
maybe my calculator is 
same
either way the program accepts the answer
thanks for help 👍
yeah its my calculator sorry
yw
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what am i doing wrong here
it seems okay to me
for some reason the stupid grader thingy thinks its wrong 😭
it might be because your lines end at -5 and 5, but i dont know if thats just the bound youre actually able to draw in
i think that might be the reason since ive clicked "Get a similiar question" multiple times and its always consistently 0.67 out of 2 when it says i get it wrong
but i cant draw anything farther then -5 and 5 which is weird
have you used the third draw tool under the graph? it looks like it's for drawing rays
that makes sense cuz that score implies that it thinks only one part out of 3 is right
yes
lol @latent walrus i'm amazed you noticed that, the difference in the picture is so tiny
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I need some help w statistics
I am working on transformations
of pmfs
here is the problem:
and here is my work
@silk sparrow Has your question been resolved?
no
What does pmf stand for
$p_Y(x) = P(\underbrace{Y}_{=X^4} = x) = P(X = \sqrt[4]{x}) = p(\sqrt[4]{x})$
M8732
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is that correct @slate zephyr ?
1^4 , 2^4, 3^4,
you could say y is fourth power of integer for example
or you could say that fourth root is an integer
is my conclusion correct that the probability of X = positive is zero
no
sorry for the confusion
okay so this is right
by definition X is negative integers
but Y is positive integers
Okay so I just need to change my possible values for Y and state that y is a fourth power if an integer
thanks for taking the time to look into this and help me out! god willing I hope to be able to pay it forward (someday)
but the sequence 1, 16, 81 is not particularly clear
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Why pay when you get it for free here 
you are welcome though
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apparently this is incorrect idk how
You took +- once you isolated, but you have to take +- when you take the sqrt in the first place, then finish isolating
i still dont understand what to put as the answer, i have one submission left
In particular, +-sqrt(A/P) = 1 + i/100 does not mean that +-(sqrt(A/P)-1) = i/100
You did the second one
But it is wrong
so it should be..
It should be ... you that computes it
like so?
isnt that the same answer u tried
what he is trying to say is that
A/P = (1+(i/100))^2
+- sqrt(A/P) = 1+(i/100) this is correct
the +- is only with the sqrt and not with the entire answer
should i remove the negative sign in front of 100 in the second answer? is that what you are referring to?
sorry my english isnt good.
@round stag Has your question been resolved?
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I have a question again
Let's persay the 39# is considered point E
Within this problem the professor actually used Position vecotr AD to compute the moment
Can I use Position AE as Position Vector?
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I got here
your handwriting is shit
I agree
you have somehow managed to make the symbols a, 4 and 9 look identical
anyway
what is i^2?
4i^2?
Aaa, an algebraic expression?
ok that's only technically correct.
i is supposed to be the imaginary unit here.
do you know what that is
Noooo...
Nooo lol
bruh what
how are you getting assigned this problem then
if you do not even know what it says
Haven't started school yet, trying to get ahead a bit
Wait are u talking about i like √-1?
yes
I dont think that has anything to do with matrices in this problem lol
They used i as an expression im 90% sure
Okay wait lemme do that math using i as -1
Holup
matrices don't inherently have to be filled with real numbers, you know.
but here this i is front and center in yours
Dunno, new to matrices lul
Okay it worked but i dunno how to articulate this
and the question hasent said anything about i being imaginary either 🤔
Thanks anyways
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hi i had these two problems i needed help with
What are those problems?
Sorry it wasn’t uploading
I am supposed to use dimensional analysis
I do have a reasoning
If we look at RHS, we see that dimension of [a] = [x] and Overall dimension of RHS is [a^n] or [x^n]
On the right hand side, we’ll have the dimension would be [log x] which has to be dimensionless
[a^n] = M^0 L^0 ^ T^0
So n = 0?
Is my reasoning correct?
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Is this the correct way to prove?
This is valid, yes
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If f(x) is non-negative and it's sum over all its finite or countably infinite no. of x values in the domain is 1, then f(x) can serve as a probability mass function of a random variable X.
How do you prove this? The text says that this follows immediately from discrete probability postulates but I don't see how. The converse is good with me. Just this.
well like... you can just construct a random variable whose PMF is f(x), no?
but how is that so apparent that the text just says "immediately" ?
here's an example
let $f(x) = \begin{cases} 0.1 & x=2 \ 0.4 & x=7 \ 0.35 & x=11 \ 0.15 & x=21 \end{cases}$
Ann
showing that you can construct a random variable with PMF=f(x) is not so easy, so as to just skip its proof. Atleast that's what I think.
the random variable X with this function as pmf
is the random variable which takes the value 2 with probability 0.1, 7 with probability 0.4, 11 with probability 0.35 and 21 with probability 0.15
that's it.
can you please talk me through the three postulates that a probability measure/function has to satisfy in order for this to work? That is, to talk me through how this situation satisfies/we can make it satisfy the three axioms
I do want to say that a big part of my question is clear now. Just this now.
you want to go down all the way to the axioms...?
i mean if you're saying this is a random variable, then it has to have a vaild probability measure/the probability function P. right?
sure i guess
because an r.v. is defined on the basis of a sample space and a sample space is defined along with a probability function, as far as I understand
formally a random variable is a measurable function from a sample space Ω to the real number line.
so like
to give you a sample space specifically tailored to our random variable
let Ω = {a,b,c,d}, F = 2^Ω, and the probability measure defined by assigning to the points a, b, c and d the weights 0.1, 0.4, 0.35 and 0.15
ok..
does this satisfy you or do you want to spend 3 hours wading through the formal proof that all the axioms are satisfied?
it's going to be very unenlightening.
can you state the non-negativity axiom for me..?
P(E) ≥ 0 for all events E
do you just make the P defined to have the additive axiom?
does it really take 3 hours?
i don't know, i did not count.
but maybe you want me to list out all 16 values of P because you won't believe me otherwise.
but we have already put a restriction on P right? cuz, we said X has this specific PMF . so we are putting another restriction on P now?
maybe
P(∅) = 0
P({a}) = 0.1
P({b}) = 0.4
P({c}) = 0.35
P({d}) = 0.15
P({a,b}) = 0.5
P({a,c}) = 0.45
P({a,d}) = 0.25
P({b,c}) = 0.75
P({b,d}) = 0.55
P({c,d}) = 0.5
P({a,b,c}) = 0.85
P({a,b,d}) = 0.65
P({a,c,d}) = 0.6
P({b,c,d}) = 0.9
P({a,b,c,d}) = 1
here is the probability measure i define on my 4-point sample space
but this does not satisfy the additive axiom
you claim so?
P{a,b} = P{a} +P{b}..
yes/no question
yeah
ok, then give me a pair of events E and F, disjoint, s.t. P(E ∪ F) ≠ P(E) + P(F).
maybe i fucked up my arithmetic somewhere.
oh yes, i did.
hold on.
do you maintain your claim?
you haven't edited it yet though..
yes i have
oh..ok
do you claim that the measure P that i just wrote out in FULL doesn't satisfy additivity? Y/N
no, I'm completely satisfied
but do you have an idea as to how you would prove this in general? I tried to but how is the proof so trivial still gets me.
i mean like
I meant to say, Yes
no..
bruh
ok
so like
anyway
let x_1, x_2, ... be the set of values at which f(x) > 0. by assumption this set is at most countable and so can be viewed as a sequence, whether finite or infinite.
especially they say it immediately follows from the postulates
ok..
construct a sample space Ω of as many points as needed
assert P({x_n}) = f(x_n)
then extend P by additivity
since $\sum_n f(x_n) = 1$ you will get $P(\Omega) = 1$ just fine
Ann
you mean P(X=x_n)=f(x_n)
there's no X yet.
but P is a set function..
i mean you can make the points in the sample space formally different from the numbers x_n
i mean {x_n} as in the event consisting of the single point x_n
ok so you mean P{w_n} = f(x_n)?
sure.
ok..
since you wanted to correct me so badly
on an inane and trivial point, i must add
but like
ok fine
P({w_n}) = f(x_n)
and then extend that by additivity to all subsets of Ω
and then X : Ω -> R will be defined by w_n ↦ x_n and it will have the required pmf
so the additive extension guarantees that any subset will also probabilistically be non-negative , I guess?
the probability of any subset will also be nonnegative
on a personal note, do you really think this follows immediately though?
my doubt is cleared btw. Good explanation i must say
yes
because all of these constructions are... less intimidating than the notation might make them appear
oh..have you seen other texts like this where they say immediately follows, but is even more not-so immediate than this?
do they get progressively more "skip obvious steps" and along with that, do you also get used to it?
i guess so
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Yo i’m stuck trying to understand besides identity
bedouts
besouts
BESOUTS
BEZOUTS
this one
I understand that d will divide ax + by
but not that d = ax + by
would love some help
there EXIST x and y such that ax+by is exactly d
if you want, give me two integers and i will tell you their GCD and a bézout expression for it
Well that’s the whole point of bezouts identity
You can look at the proof
well ye
i’ve looked at a bunch of proofs i don’t get them
i just coke across stuff like this that seemingly uses the proof to prove itself
yaa but why
it would just be helpful to work through a proof with someone
brb
ight
ok im back
so like do you want to work through a pre-written proof or do you want a demonstration with an example
i think this would be better 🙂
ok
give me two integers
any two, but preferably ones not equal to each other nor zero
11 and 64
Result:
-1
do you have a proof that you're reading somewhere?
i haven’t been given one formally no
can you share at least one of the proofs you looked at
ye sorry i’ll just be a few minutes
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✅
@bright geyser ya still there or what
sorryy, I think I actually found a proof
this one was a little strange but it did make sense to me
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no just cos
?
in a triangle
what?
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!status
What step are you on?
1. I don't know where to begin
2. I have begun but got stuck midway
3. I got an answer but I'm told it's wrong
4. I got an answer and would like my work checked
5. I have a question about someone else's worked solution
6. None of the above
2
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Show your work, and if possible, explain where you are stuck.
forgot about it
i need to prove that the initial equation has no roots
and/or that my polynomial equation has no root in the interval [0; 1]
i ment the simple cos
you took t = sin^2(x) yes?
yeah
so that means t ranges from 0 to 1
yes
and from the graph you see the function has no zeros between 0 and 1
exactly
how old are you
but i cannot graph this on a piece of paper because it's too complicated
me? why does that matter?
are you going to help
or are you just gonna keep interrupting
bc so far you've said nothing that was helpful or relevant to the question at handd
and OP's age is not relevant either
good for you but nobody asked your age
who asked
nnnnnn
anyway ok so like
i need to prove that the initial equation has no roots
hm
yeah
can we come up w/ some clever bounds here
cos^6(x) + sin^8(x)
what can we do to this
ofc but why do i need them
the only thing i've come up with is to find the derivative, then determine the point where f(x) is the smallest
overkill imo
but as i said it didn't help due to me not being able to solve the cubic equation f'(t)=0
oh this is EASY actually
what do you suggest?
$\sin^8(x) \leq \sin^2(x)$ and $\cos^6(x) \leq \cos^2(x)$
Ann
so lhs ≤ 1
uhmmm interesting
but it doesn't prove anything
as far as i can see
i mean like
i understand what you mean but mathematically for this to mean something sin(x) and cos(x) have to be equally monotonic
???
you don't need any monotony for shit
these two inequalities imply that FOR ALL REAL $x$ we have $$\sin^8(x) + \cos^6(x) \leq \sin^2(x) + \cos^2(x) = 1$$
Ann
therefore $\sin^8(x) + \cos^6(x) \leq 1$ for all $x$
Ann
i agree with what you're trying to say but disagree with your conclusion
1>5/4 ?
not that
this
i know it's true but that's definitely not how you prove it
for all real numbers $a, a', b, b'$ if $a \leq a'$ and $b \leq b'$ then $a+b \leq a'+b'$
Ann
agree or disagree?
I agree but sin(x) and cos(x) are not constant numbers, they're functions
for every x in [0; 2pi] they vary
this reasoning applies to them all the same just with a ∀x ∈ R stuck to the front
and the inequality is true pointwise
can you find a value of x when $sin^8(x)>sin^2(x)$
Joseph.P
okay Ann i have a question for you
hit me
how do you prove $$2cos(x) + 5sin(x) = 8$$ has no solutions
exterminated
$|2 \cos(x) + 5 \sin(x)| \leq 2 |{\cos(x)}| + 5 |{\sin(x)}| \leq 2 \cdot 1 + 5 \cdot 1 = 7$
apply triangle inequality
Ann
or even simpler
or Caushy Swartz inequality
its not because max(cos(x)) == max(cos(x)) = 1 right?
what
bro i'm in high school
i never spoke about maximum
uhm okay
sorry, can you restate your question to me
because it looks like you take issue with the proof i just presented but i do not know what your issue is
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what.. im lost and idk how to do any of those..
Be it a , b > 0 . Demonstrate the unequals ?
the stuff inside () is just a few tips in order to help us
but idk anyhting
with the first question, how could you make the inequality easier to prove
well i could multiply the 2 with the a2+b2 and the 1 with the shorted formula that i got below ?
or idk
which formula?
since i could probably make the a2 + b2 into this form
uhm a^2 +_ 2ab + b^2
$2(a^2+b^2)\geq a^2+2ab+b^2$
chlamydia
is this what you mean?
yeah..
right, so where can we progress from here?
having terms on both sides of the inequality is a bit inconvenient
sorry but what do you mean by terms ? since english is my second language i dont really understand a lot of stuff
all the a and b
ah
i'll be careful
we could make it 2a^2 + 2b^2 and then we could substract ? ( - ) a2 and b2
but idk if it'll head us towards a dead end or not
chlamydia
does this look familiar?
i mean it does..
so we just redo the formula said previously?
and we end up with (a-b)^2 ?
$(a-b)^2\geq0$
chlamydia
and because it's squared, it's always true
wait that was it ?
wait but how did we substarct the a and b from this and got this outcome ?
or
nvm
nvm
we moved the 2ab as well in that process
with the changed symbol
so what's the obvious problem in 2?
sure
ye that will probably be the way
$\frac{a^2+b^2}2\geq\frac{(a+b)^2}4$
chlamydia
chlamydia
you can see where i got this?
yeah, and expand (a+b)^2
yeah
and now...
now it is just like last problem.
a^2 + b^2 - 2ab >_ 0
i think
$a^2+b^2 - 2ab\geq 0
Hi
$a^2+b^2 - 2ab\geq 0$
chlamydia
so this is also right ?
Would you be free to help me out with a question
yeah
alright , thanks
typically you'd need to go to #❓how-to-get-help
the teacher gave a tip of " at end 2 can be given as a common factor"
what does that mean..
maybe it's talking about multiplying the 2 to simplify?
probably
but we didnt need it
so it's alright
this is where i tried and failed so hard
but i'll try
did you square both sides
and you get a nasty right side
but because you have ab on both sides, you can do something with that first
idk what we can do.. the only thing i thought of is multiplying both sides by (a+b)^2 to get rid of that from the right side
sure, but we can divide by ab too
yeah that also but idk how to do that
$(a+b)^2\geq ab$
chlamydia
why not
since dividing was an option.. but how do we divide the terms?
i've never done this so idk how it's done
how do i divide 2a to a ? it'll give 2 ?
$ab\geq \frac{(ab)^2}{(a+b)^2}$
chlamydia
what 2a
it was an example
oh yeah
dividing it all by ab ?
yes
because a,b>0, you can multiply or divide with no problem
when you divide 4 by 4, what do you get?
you are dividing (ab)^2 by ab here
that's where i had troubles.
what do you mean?
i dont understand how i can divide them since they aren't numbers
i know the principle but idk the way
i wouldn't say they aren't numbers, it's like they're pretending to be numbers
so ab represents a number
but it is squared
yeah
so when you divide that by ab
what is this
1*1
you only divide by ab once
2?
like if you have 7^2 divided by 7
it's 7
so we get ab?
yes
General.Admiral MWstudios
so 1 >_ ?
chlamydia
right?
chlamydia
yeah
yup
$(a+b)^2\geq ab$
General.Admiral MWstudios
then we simply move it to the left
i'll tell you now, you can't use the same trick
$a^2+ab+b^2\geq0$
chlamydia
it's ok
so we simply - it from the expanded left side
since it was positive , we extracted it from the left row
right?
yes
and we cant do anything with this
so we simply leave it as it is?
i mean we got what we wanted
yeah, there's no good way to factorise it
i think this is good
yeah
well
chlamydia
so you but it all on ()^2 ?
yes
so we get (a+2)^2 which is already a formula and it'll surely be used . on top of a+1
so it'll remain the same?
like we remove the a+1?
idk how we got rid of it
i mean we got (a+2)^2 on top from the ()^2 . but on the lower part we got a+1
$\frac{a+2}{\sqrt{a+1}}\geq2 \Rightarrow (a+2)\geq2\sqrt{a+1}$
chlamydia
$(a+2)^2\geq 2^2(a+1)$
chlamydia
ohh so we moved itt
this is the first time i see someone move from the left to the right
it's not about left or right, it's about different things that make work hard, like fractions or square roots
alright
it does make sense now
so now we simply open the left side
a^2+2ab+4 >_ 2^2(a+1)
i mean the formula is (a+b)^2 = a^2 + 2ab + b^2
yes
so replacing that will be
and this time, b=2
oh lol
$a^2+4a+4\geq 2^2(a+1)$
General.Admiral MWstudios
yup
so it gives us $a^2\geq 0$
General.Admiral MWstudios
right?
yes
this one is special, because you have a pattern
yeah..
the upside down a?
yeah
it means for all
ah mb
$(t-\frac1t)^2\geq0$
chlamydia
i want you to think about this
and see if you can get something nice out of it first
i need to compare both of them
ah
you good?
did you expand the left?
ah
$2t*\frac1t$
General.Admiral MWstudios
take your time
yeah that's right
since if we replace t with any number other than 0
i mean greater than 0
it'll give us 2
for example 3
yeah, because you have t and you're dividing it away
2* 3 multiplied by 1 and 3 it is 6 mult. 1/3 is 2
it's ilogical and logical at the same time
chlamydia
$t^2+\frac1{t^2}\geq2$
chlamydia
what do you mean
oh, don't worry about that
and get t^2 + 1 / t^2
this is the big part i wanted you to see
if we look back at the question
$(x+1)+\frac1{x+1}\geq2$
..
do you see something similar?
chlamydia
damn.
this tells us that anything+1\anything>=2
for positive numbers
yeah..
no, it's because of this being true
x
yeah it'll be easier..
yeah maybe it wasn't good to try to teach that
what?
try to teach what
this
we could've just done multiplying
but that comes in useful for harder questions
i'll end up using it as well since im on math and comp science profile..
$(x+1)+\frac1{x+1}\geq2 | * (x+1)$
so we end up with
nvm
multiplying mbb
General.Admiral MWstudios
about the middle term
i noticed it as well
General.Admiral MWstudios
wait wtf
chlamydia
right?
ah yes
so you have x+1, and you're dividing by itself
so we get 2 ?
please think carefully about this, if you have a number, and you divide by the same number...
we get 1 ?
yeah
pls where can i find help 0
so we got x+1 / x+1?
yeah
we multiplied only the upper part
she already has a channel open lol
that's alright
right?
right**