#help-36

1 messages · Page 235 of 1

soft zealotBOT
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Prathmesh

dreamy warren
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you used $dt/dx = -(1/v^2)(dv/dx)$ right

soft zealotBOT
dreamy warren
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i think you have an extra v^2 on the left

final saddleBOT
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@boreal smelt Has your question been resolved?

boreal smelt
boreal smelt
dreamy warren
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okay yeah i was wondering if i was wrong 😭

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the equation should be linear in v

boreal smelt
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i am sorry

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😭

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thanks btw

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warm python
#

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.

soft zealotBOT
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waimas

dreamy warren
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yes the method looks correct

desert mantle
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except for the typos

robust mulch
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match variables

warm python
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cool

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thanks

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torn heart
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\int_{-\infty}^{\infty} e^{-t^2/2} dt = \sqrt{2\pi}
why

torn heart
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$\int_{-\infty}^{\infty} e^{-t^2/2} dt = \sqrt{2\pi}$

soft zealotBOT
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Chilll

ionic venture
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What have you tried so far?

torn heart
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i found the solution

signal vector
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Oh, your screenshot appears to be from the same page

ionic venture
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Gauss hiding behind 1.414

opal plinth
# torn heart

That's not the same expression, but you can just make a change of variable

ionic venture
# torn heart

After working out the integral, you would need to figure out how you could turn..

ionic venture
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$e^{-\frac{t^2}{2}}$ to $e^{-x^2}$

torn heart
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it gives sqrt(2pi)

soft zealotBOT
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Erebus

signal vector
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Not much to figure out there

ionic venture
final saddleBOT
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tacit dust
#

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.

tacit dust
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Can someone check my sol?

leaden moon
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,rccw

soft zealotBOT
tacit dust
leaden moon
soft zealotBOT
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1 divided by 0 equals Infinity

tacit dust
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Pythagorean theorem

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on triangle OMD

leaden moon
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makes sense

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it's correct

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giờ thì đi kết luận là xong =)))

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!done

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tacit dust
leaden moon
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=)))

tacit dust
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thêm 1 ng việt trên đây 🙂

leaden moon
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m nghĩ sao t hiểu đc bài của m

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=)))

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!done

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tacit dust
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.close

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sharp wing
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how do u solve part b

final saddleBOT
sharp wing
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hold on ill jump to a new channel

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bleak notch
#

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.

whole halo
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what Im thinking is theres ways to explain the bayes formula or to make it plain obvious in other examples

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maybe you look up a few videos, then try and use their words on this problem

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Im just thinking if the ball was black, theres no way transferring a white ball is going to help the odds

tired walrus
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or maybe you could draw a tree diagram for it idk

whole halo
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but if the ball is white...

bleak notch
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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

whole halo
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...why is my drawing program drawing different thicknesses for differenc olors

bleak notch
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there would be flying cars in 2025 they said

whole halo
bleak notch
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I'm not really sure if I'm getting my question across well

bleak notch
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but something that bothers me is that observing something afterwards "affects" the probability in retrospect

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if that makes sense

whole halo
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oh thats all?

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if it didnt, itd be 50%

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if it did, itd not be 50%

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thats it

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you can see theres more white balls available in one of the options

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so when you choose a white ball, its more likely its the top one

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and so its more likely that a white ball was transferred than a black ball

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indirectly because a black ball leads to fewer of the outcomes

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and also indirectly because a white ball leads to more likely outcomes than a black ball

bleak notch
# whole halo if it didnt, itd be 50%

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?

whole halo
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thats not true

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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

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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)

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similarly you just found out the ball is white

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youre saying that tells you nothing about the state of transferring the ball?

bleak notch
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so in some sense, it's correct to say that the future affects the present?

whole halo
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inuka use that common sense

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the present lets us know about the past

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thats called history

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you did history pulling a white ball and then thinking about what mustve happened to let that happen

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if youre pulling balls out, thats not the future either, thats the present

whole halo
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same argument works there too

bleak notch
whole halo
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..as opposed to how many observations?

bleak notch
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that's interesting yeah

whole halo
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any observeration is usable information

bleak notch
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if we took 10 observations with replacement then it seems like it tells us something

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but then if you just reduce the amount

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surely 1 tells you something

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that's very strange to me

whole halo
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then what was even the point here

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we cant get much out of 1 ball

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but its bold to say you get nothing

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not even a little bit of information? we saw the ball

bleak notch
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ok that's fair

whole halo
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you can split up the cases like this

bleak notch
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since we're factoring that information into our calculation, surely that means we can quantify how much information a single observation gives us

whole halo
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oh thats not good in dark mode

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I dont know entropy so Im not answering that

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as for this,

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if upon seeing a white ball you guess that a white transfer mustve happened, you have a 4/5 chance of getting it right

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this is because in two of the three scenarios, you were given more white balls to infer such

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a white transfer directly boosts the chances to have picked a white ball

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and so the chance changes, and moreover gets higher

bleak notch
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oh interesting, so it's something like the sub-state-space that we select from is larger

whole halo
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if on the other hand any white transfers never ended up in the second urn,

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history is repeating itself, put that background back

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you can see youd still have the usual 2/3 chances

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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

bleak notch
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ok that's kinda interesting, I'll play around with this for a bit

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thanks for the help

whole halo
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np

bleak notch
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barren pebble
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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?

tranquil pine
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(or what equivalent facts do you know about it)

barren pebble
barren pebble
tranquil pine
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yay finally one person who defines it like that

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do you know inversion?

barren pebble
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I know the definition of that

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Through some weird (kinda famous) proof of Ptolemy's theorem

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But i'll prefer not to use it

tranquil pine
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hmm ok well yeah actually we don't need that

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lol

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because you can just angle chase

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Do you know <BHC in terms of the angles of triangle ABC?

barren pebble
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∠BHC = 180°- ∠HBC - ∠HCB=180°-(90°- ∠B)-(90°- ∠C) = ∠B + ∠C

tranquil pine
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ok that's good

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you want to show <BPaC is the same

barren pebble
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Oh lol

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Got it

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I'm so dumdum sad

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Thank you i guess

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tranquil pine
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lol yw

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the reason I mentioned inversion was because a lot of properties about the humpty (and Dumpty) point are very easy to prove with inversion

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its not needed in this one but it makes other properties much easier to prove

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so when you learn inversion you can try to come back to this config and prove other properties with it

barren pebble
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Thanks

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Today is the first day i learn about those points though, i guess i'll stick to the basics

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lunar cairn
#

"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

leaden moon
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you got any revision or smth like that?

lunar cairn
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What particular YouTube channel or topic would you recommend

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Or other tips

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@lunar cairn Has your question been resolved?

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final saddleBOT
craggy plank
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light belfry
final saddleBOT
light belfry
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Ya I am pretty sure this problem is nonsense

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Cuz AEC is essentially AEB

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currently trynna see this problem assuming BE is not a straight line

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(But yea assumign that how would I know which one is straight and which one is curved

next thorn
hearty tide
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Dammn

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Question is hella wrong

light belfry
hearty tide
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I see typo

light belfry
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Yea , ig 25 is CAD

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but you can easily find that

next thorn
next thorn
light belfry
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Ty

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guys

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Just wanted to confirm that I am not going senile

hearty tide
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Let's try for ACB and check if any option matches, ig.

light belfry
hearty tide
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Angle ACB

light belfry
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Yea that'show I found out question is wrong

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.close

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torn ore
#

How to find this limit ?

final saddleBOT
torn ore
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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 .

blazing nymph
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Well as n tends to inf, the +1 and -1 will become insignificatn so how else can u write the limit?

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yep

final tangle
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careful with ()

torn ore
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How do I factor out the (2n) if there is an exponent, lets say top left

final tangle
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you want
(2n)^3
etc

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wdym factor out

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just expand/simplify applying exponent laws

full jungle
torn ore
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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?

robust mulch
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(2n-1)^3=(n(2-1/n))^3

full jungle
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$\left(2n-1\right)^{3}\ =\ n^{3}\left(2-\frac{1}{n}\right)^{3}$

torn ore
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oh, i jst keep it like that facepalm

soft zealotBOT
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Xerxes

torn ore
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I see. thanks

next thorn
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top and bottom

full jungle
torn ore
#

.close

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warm python
#

I don't really get this

final saddleBOT
warm python
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The justification that is

left echo
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Again

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What is an MLE?

warm python
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The value of the parameter that maximises the joint dit

scarlet sequoia
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so the value that maximizes L(theta)

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L(theta) only has two values, 0 and (1/2)^n

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since (1/2)^n is the max

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any value of theta that gives you L(theta) = 1/2^n is an MLE

left echo
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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?

warm python
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I didn't mean to close the channel rudly last time , sorry

scarlet sequoia
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so intersection is {2theta <= min(x_i) <= max(x_i) <= 3theta}

left echo
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Ah

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Right, the function is in θ

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That's pretty cool

warm python
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That's all for now. Can I close the channel pls

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.close

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blazing kindle
#

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) 0

The 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.

tired walrus
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for vectors in general,

uv = |u| * |v| * cos(theta)

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where theta is the angle between u and v

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@blazing kindle

blazing kindle
tired walrus
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in an equilateral triangle the interior angles are always each 60°

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the angle between vectors AB and BC is 180 minus that

blazing kindle
#

i see

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tysm

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torn dome
#

prove that r is irrational if r^3 + r + 1 = 0

final saddleBOT
torn dome
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suppose r is rational

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r = p/q

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now $r^3+r+1 = \frac{p^3}{q^3} + \frac{p}{q} + 1$

soft zealotBOT
#

Sean [Ping On Reply Please!]

leaden moon
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step 1: solve the cubic

torn dome
#

what now

leaden moon
torn dome
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i am a nub idk if that was sarcasm

leaden moon
soft zealotBOT
#

1 divided by 0 equals Infinity

tired walrus
torn dome
#

yeah

torn dome
leaden moon
torn dome
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ok so $\frac{p^3q + pq^3 + q^4}{q^4} =0$

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where is the dumb bot

tired walrus
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why 1 on rhs

leaden moon
tired walrus
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also you shouldnt have put a space after the first dollar

soft zealotBOT
#

Sean [Ping On Reply Please!]

tired walrus
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you could have used q^3 as your denom

leaden moon
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having the denominator is scary

tired walrus
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p^3 + pq^2 + q^3 = 0

torn dome
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$p^3 + pq^2 + q^3 = 0$

soft zealotBOT
#

Sean [Ping On Reply Please!]

torn dome
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now do i have to solve this

leaden moon
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for strongness

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idk what to call that

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$p \in \mathbb Z$, $q \in \mathbb N$, $(p, q) = 1$

soft zealotBOT
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1 divided by 0 equals Infinity

tired walrus
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you don't have to "solve" this per se

torn dome
tired walrus
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also yes it will be good to start off with r=p/q in simplest form

leaden moon
torn dome
tired walrus
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this eq rearranges to q^3 = p(-p^2 - q^2)

leaden moon
torn dome
soft zealotBOT
#

Sean [Ping On Reply Please!]

torn dome
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alright

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now how to proceed

tired walrus
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p and q are coprime

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and now you see p divides q^3

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how can this be

leaden moon
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🔥

torn dome
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contradiction?

leaden moon
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$p = q = 1$ satisfies tho

soft zealotBOT
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1 divided by 0 equals Infinity

torn dome
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then what

leaden moon
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but if you substitute back $p = q = 1$ then that does not satisfy the equation

soft zealotBOT
#

1 divided by 0 equals Infinity

leaden moon
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$p = -1$, $q = 1$ also satisfies this, but try to plug back into the original equation

torn dome
soft zealotBOT
#

1 divided by 0 equals Infinity

leaden moon
torn dome
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so are we done

leaden moon
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yeah that completes the proof

torn dome
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so if (p,q) = 1 then p not | q?

leaden moon
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as i said before p = q = 1

torn dome
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except that ig

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it holds true

leaden moon
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and except p = -1, q = 1

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and except p = 1, q = -1

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then it's true for all the remaining cases

torn dome
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can we do this by breaking into cases

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cases such as p is even and q is odd

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and p is odd q is even

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then both odd, etc

leaden moon
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p even q odd

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and vice versa

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eh?

torn dome
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yea

leaden moon
soft zealotBOT
#

1 divided by 0 equals Infinity

leaden moon
leaden moon
soft zealotBOT
#

1 divided by 0 equals Infinity

leaden moon
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which i believe if you try to substitute in your $r^3 + r + 1 = 0$ then it does not satisfy

soft zealotBOT
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1 divided by 0 equals Infinity

bold turtle
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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

leaden moon
#

,w solve r^3 + r + 1 = 0

leaden moon
#

proof done KEK

torn dome
#

give me another proof question like this

leaden moon
#

ooh

bold turtle
#

prove that sqrt(2) is irrational

leaden moon
torn dome
#

thats the first prove they teach in a discrete math class

leaden moon
#

Prove that $\forall k \in \mathbb N$ that is not a square number then $\sqrt{k}$ is always irrational

soft zealotBOT
#

1 divided by 0 equals Infinity

leaden moon
#

how about now

torn dome
#

(idk how to do it)

torn dome
#

i will use contraposition

leaden moon
soft zealotBOT
#

1 divided by 0 equals Infinity

leaden moon
torn dome
#

no contraposition

leaden moon
#

ahhhhhhhhh

bold turtle
bold turtle
#

Assume the opposite i.e. that your answer is rational; arrive at a contradiction

torn dome
#

root k is always rational for all k belong to N that are squares

bold turtle
#

Starting with that, and then showing sqrt(p) is irrational for any p prime, is good practice

torn dome
#

if root k is rational then k is a square

leaden moon
torn dome
#

root k = p/q

leaden moon
#

so you arrived at a contradiction that fast

torn dome
#

k = p^2 / q^2

leaden moon
#

and (p, q) = 1

#

k is a natural number

torn dome
#

k = (p/q)^2

leaden moon
#

so $k = p^2$

soft zealotBOT
#

1 divided by 0 equals Infinity

torn dome
#

k = n^2 for some n = p/q

#

so k is a square

leaden moon
#

aight i see

torn dome
#

is this valid

leaden moon
#

now generalize this for every nth root

#

n >= 2

torn dome
#

wat

bold turtle
torn dome
leaden moon
#

yeah enough of the roots

torn dome
#

proof by contraposition

bold turtle
#

"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

bold turtle
proper dagger
#

there is a rather nifty argument using parity

leaden moon
#

that's why the $\gcd(p, q) = 1$ assumption is so important

soft zealotBOT
#

1 divided by 0 equals Infinity

proper dagger
#

but I would rather not spring that on OP atm

leaden moon
bold turtle
#

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 ]

torn dome
#

how is it called contradiction, i took the contrapositive of the original conditional

#

then i proved the contrapositive

leaden moon
#

Contradiction is when you want to prove the opposite is wrong

torn dome
#

i proved that the contrapositive is true

bold turtle
leaden moon
#

what you did here is contradiction

torn dome
leaden moon
#

it's a contradiction

torn dome
#

k = n^2

bold turtle
torn dome
#

so k is a square

bold turtle
#

You HAVE NOT done that yet.

proper dagger
leaden moon
soft zealotBOT
#

1 divided by 0 equals Infinity

torn dome
leaden moon
torn dome
#

(p,q) = 1

proper dagger
#

if p/q is not an integer, then how can k be a perfect square?

leaden moon
#

p/q is only a rational number

bold turtle
leaden moon
#

ragebait ahhhhh

bold turtle
#

am I using non-standard terminology or sth wtf

leaden moon
proper dagger
#

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

torn dome
proper dagger
#

unless the rational happens to be an integer, but not the case here.

#

at least you've not shown that to be the case

leaden moon
bold turtle
#

Yeah, so, you CAN solve this by proving
root(k) is rational => k is a square (of an integer)
but this isn't done

leaden moon
#

prove that an irrational number + a rational number always results to an irrational number

torn dome
#

ok i suppose k is rational

#

then k = p/q

bold turtle
#

No...

#

Okay

torn dome
#

how can k be a square

torn dome
#

its a fraction

bold turtle
#

You need practice at figuring out what it means to say something is rational or not

umbral steppe
#

the contrapositive method is really not the best method to attack that particular problem.

bold turtle
#

So start with 1/0=inf's question

umbral steppe
#

it is very hard to show that q = 1.

torn dome
#

then i give a counter example of root 2 and 1

leaden moon
torn dome
#

root 2+ 1 is irrational , contradiction

#

proved

leaden moon
#

||i go by Infinity||

leaden moon
#

💀

silver dew
#

You can’t prove things by examples

#

You disprove it by a counterexample

torn dome
#

ok i assume that rational + irrational is rational

i am disproving my assumption

bold turtle
umbral steppe
#

Sean, have you learnt about quantifiers?

bold turtle
torn dome
#

how do i express an irrational number?

umbral steppe
#

be aware of the quantifiers of the statement you want to prove.

torn dome
#

rational i can do with p/q

bold turtle
#

Those aren't quantifiers...

silver dew
#

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

torn dome
#

a + b = p/q

#

a is rational

#

b is not

umbral steppe
#

you can only use an arbitrary counterexample if your quantifier is $\exists$, not $\forall$. $\forall$ requires a stronger argument.

soft zealotBOT
torn dome
#

alright im stuck

leaden moon
#

well, since one of them is rational

torn dome
#

where to go from a + b = p/q

leaden moon
#

assume $a$ is rational

soft zealotBOT
#

1 divided by 0 equals Infinity

torn dome
#

ok

#

ok i got it

#

i have to take difference

#

with the p/q

#

b = m/n

#

contradiction

bold turtle
#

Contradiction because...?

umbral steppe
#

may I know if you're doing discrete math, number theory, analysis, or something else?

torn dome
torn dome
bold turtle
torn dome
umbral steppe
silver dew
#

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

leaden moon
#

i miss the xmas icons

torn dome
#

a + b = p/q
r/s + b = p/q
b = p/q - r/s

bold turtle
#

I can't prove to you that I've bought apples without showing you the apples I've brought

leaden moon
torn dome
#

take the lcm or smth

bold turtle
#

Show that p/q - r/s is rational

torn dome
#

b - ps - rq)/rs

torn dome
#

rs is also integer

#

rs != 0

#

so it is rational

umbral steppe
#

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.

leaden moon
umbral steppe
#

this does require you to recall what prime factorizations are and what a perfect square means in terms of its prime factorization.

leaden moon
#

what is $v_p$ here 😭

soft zealotBOT
#

1 divided by 0 equals Infinity

leaden moon
#

no need

worldly mesa
#

p-adic valuation

leaden moon
#

$nb^2 = a^2$, this means that $b^2 \mid a^2$

soft zealotBOT
#

1 divided by 0 equals Infinity

leaden moon
#

and $\gcd(a, b) = 1$

soft zealotBOT
#

1 divided by 0 equals Infinity

torn dome
#

contradiction

leaden moon
umbral steppe
torn dome
leaden moon
umbral steppe
#

it was meant to be an example to get OP to see the kind of structure that is expected of a proof.

torn dome
leaden moon
#

anywys

bold turtle
umbral steppe
#

but if you insist on it, I'll remove the proof, and I apologize for sending a complicated proof here.

leaden moon
#

anyways, this is just an example on how you can write your proof @torn dome

leaden moon
#

oh mb im too late

torn dome
#

can you guys give me another question

#

proof question

gleaming anchor
#

in discrete math, or are you ok with other fields?

gleaming anchor
#

sure, let me get one from my stash

torn dome
#

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)

bold turtle
#

"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

gleaming anchor
#

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.)

bold turtle
gleaming anchor
#

hint: use the algebraic definition of an odd number.

torn dome
#

your role says undergrad

bold turtle
#

CS master's degree student; I've done a maths undergraduate degree

bold turtle
#

(I'm not American, so "major" is meaningless here)

leaden moon
bold turtle
leaden moon
gleaming anchor
final saddleBOT
torn dome
#

i am getting remainder = 1

gleaming anchor
#

ok not too bad of an attempt, and I presume you did your long div correctly

torn dome
#

yeah

gleaming anchor
#

but from 4k^2 + 4k + 1, you could have factored out a 4k from the first two terms to get 4k(k + 1) + 1

bold turtle
#

-# yh, tbh, I'm intrigued on what you did that you're calling long division

gleaming anchor
#

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

gleaming anchor
#

,rcw

soft zealotBOT
gleaming anchor
#

not wrong

#

but again, there's a faster and more direct method

torn dome
gleaming anchor
#

I'd prefer the factoring method because it leaves the dangling + 1 as undeniable proof

torn dome
#

are you saying that i should write $n^2$ as $4k(k+1)+1$

soft zealotBOT
#

Sean [Ping On Reply Please!]

gleaming anchor
#

yes.

torn dome
#

how can i show that there will be remainder of 1

bold turtle
#

bruh, the literal dangling 1 outside of that bracket IS the remainder

gleaming anchor
#

consider that k is an integer. that means k+1 is an integer too.

torn dome
#

yeah

gleaming anchor
#

then obviously 4k is also an integer.

torn dome
#

yuh

gleaming anchor
#

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

bold turtle
#

cf. how if you write 194 = 14 x 13 + 12, then 12 is the remainder you get when you divide 194 by 13

torn dome
#

well i could have done $4(k^2+k)$

soft zealotBOT
#

Sean [Ping On Reply Please!]

bold turtle
#

Yh you can, and that's equally valid

#

The point being, you can clearly pull out a 4, and get a remainder of 1

gleaming anchor
#

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

torn dome
#

alright

#

but my long division....

#

blobcry.

gleaming anchor
torn dome
#

cool

gleaming anchor
#

I never said it was wrong.

torn dome
#

alright

#

thanks

gleaming anchor
#

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.

leaden moon
#

woah woah woa

#

we ain't doing AM-GM here opencry

bold turtle
#

That's pretty tame compared to the full AM GM tho wdym

gleaming anchor
#

you don't need AM-GM

#

at all

#

you can, and it does oneshot the problem

bold turtle
#

In fact you're technically proving the AM-GM here for two numbers

leaden moon
#

yeah

gleaming anchor
#

but it's not necessary

#

also, sometimes the longer way is more general

torn dome
#

i arrived at p < q

gleaming anchor
#

or more insightful

torn dome
#

is that wrong

gleaming anchor
leaden moon
gleaming anchor
#

when doing proofs and wanting to get your answer checked

leaden moon
#

assumption?

gleaming anchor
#

it might help to show the whole proof

#

because arriving at a right conclusion from illogical steps renders the proof moot

#

for instance

bold turtle
#

"I have 3 apples because the spaceship man landed on the moon, and therefore I have 3 apples" is not a valid proof

gleaming anchor
#

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

topaz tusk
#

indian mathematics questions solved here?

leaden moon
gleaming anchor
bold turtle
#

!occupied - jeez does no one read the damn info file

final saddleBOT
#

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).

torn dome
#

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

leaden moon
bold turtle
# leaden moon idk

-# They're asked, and seldom solved (because of the type of question and the nature of the answers sought 😭)

gleaming anchor
#

p-q< 0
p< q
these two

torn dome
#

p < q and q < p

torn dome
#

is that wrong

gleaming anchor
#

(p-q)^2 < 0
you should have stopped here

#

this is the contradiction you're looking for

bold turtle
#

Because that should've sent alarm bells ringing

leaden moon
#

these 2 steps don't make sense

torn dome
#

i didnt use parenthesis

gleaming anchor
#

also I suppose you meant < 0 on the second line there

torn dome
#

yeah

#

mb

#

okay so (p-q)^2 < 0

#

what now

bold turtle
bold turtle
gleaming anchor
#

what do you recall about squaring real numbers?

torn dome
#

got it

#

square is positive

#

ok so proved

bold turtle
#

or...?

torn dome
bold turtle
#

ye

torn dome
#

yay

gleaming anchor
#

ok the proof works. BUT

#

since you are in uni

bold turtle
#

Try and write up a proof

gleaming anchor
torn dome
bold turtle
#

...

torn dome
#

i did one in my MSE

bold turtle
#

I'm currently mashing the X-to-doubt button fwiw

torn dome
#

i got 2/5

leaden moon
#

yo @torn dome

#

since you learned your technique

#

why don't you go and try to help #help-2

gleaming anchor
#

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

leaden moon
soft zealotBOT
#

1 divided by 0 equals Infinity

torn dome
#

i solved that one already

leaden moon
bold turtle
#

It's beneficial to see if you've actually learnt it well if you can teach it to someone too

leaden moon
#

by yourself

torn dome
torn dome
#

but i have the discrete mathematics final tmr

leaden moon
#

just come and try to help

#

ill backup

gleaming anchor
#

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

torn dome
#

@gleaming anchor

gleaming anchor
#

well written

torn dome
#

took you 10s

gleaming anchor
#

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

torn dome
#

thank you Celine!

gleaming anchor
#

rip the accent but nps

torn dome
#

saline

#

i say that

#

anyways ty

#

.close

final saddleBOT
#
Channel closed

Closed by @torn dome

Use .reopen if this was a mistake.

#
Available help channel!

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final saddleBOT
craggy plank
#

.solved

final saddleBOT
#
Channel closed

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#
Available help channel!

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Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.

torn dome
final saddleBOT
torn dome
#

how are there 2^k terms (in last step)

tired walrus
#

the denominators go from 2^k + 1 to 2×2^k inclusive

#

<@&268886789983436800> troll

young bobcat
#

wait who r u claiming is a troll

faint edge
#

@warm junco don't troll. It distracts people from getting help.

young bobcat
torn dome
#

.close

final saddleBOT
#
Channel closed

Closed by @torn dome

Use .reopen if this was a mistake.

#
Available help channel!

Send your question here to claim the channel.

Remember:
Ask your math question in a clear, concise manner.
Show your work, and if possible, explain where you are stuck.
Do not immediately ping people or roles. After 15 minutes, feel free to ping <@&286206848099549185> once.
• Type the command .close to free the channel when you're done.
• Be polite and have a nice day!

Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.

torn dome
#

what is the best method of proof for this

final saddleBOT
torn dome
#

direct proof doesnt work, i get stuck at 4k^2 + 4k

obtuse hedge
#

Can you factor 4k^2 + 4k

torn dome
terse dagger
#

yes

obtuse hedge
#

We want it to be divisible by 8, so since it has a factor of 4, what are we missing?

torn dome
#

2

terse dagger
#

there is a special property of the product you're left with

#

ignoring the 4

obtuse hedge
#

Indeed, to show k(k+1) is divisibe by 2 it is possible!

terse dagger
#

Think about what k is

#

and what that means for k+1

torn dome
#

an integer

obtuse hedge
#

With reference to division by 2 then, k, as an integer must be either _ or _

torn dome
#

if k is even,k +1 is odd

#

if k is odd k +1 is even

obtuse hedge
#

Right, so in either case, k(k+1) has an _ factor

torn dome
#

2

obtuse hedge
#

Exactly!, so k(k+1) is always divisible by 2

torn dome
#

i am proving for 8

terse dagger
#

you're left with 4 k (k + 1)

torn dome
#

yeah

terse dagger
#

and you can say that for any k

obtuse hedge
terse dagger
#

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

torn dome
#

how about we use induction on this

terse dagger
#

l being another integer

torn dome
#

btw how can i prove that k(k+1) is always even

terse dagger
#

You basically did before

torn dome
#

i could make two cases

obtuse hedge
torn dome
#

like when k is even and when k is odd

#

then i can multiply

#

okay

#

btw what abt induction

terse dagger
#

You don't need induction because for all the steps you've gone through you haven't said anything about n or k

obtuse hedge
torn dome
torn dome
# torn dome

i used to do these typa problems using induction

#

is this one also possible using direct proof or some other method

obtuse hedge
#

$11^{n+1} + (11 + 1)^{2n - 1} = 11^{n+1} + 11^{2n - 1} + 11^{2n - 2} + \dots + 11 + 1$ and $11^2 + 11 + 1 = 133$ so it should be possible to prove directly

soft zealotBOT
#

Coolempire2026

obtuse hedge
#

Likely easier by induction though

torn dome
#

how did you expand that power

obtuse hedge
#

Binomial theorem

torn dome
#

i'd stick with induction 💀

#

btw i forgot how to do it with induction

terse dagger
#

Base case

#

induction step

torn dome
#

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

terse dagger
#

So what is your base case?

soft zealotBOT
#

Sean [Ping On Reply Please!]

torn dome
terse dagger
#

which you have proven i imagine

#

that it works

torn dome
#

yeah

torn dome
#

so i am straight at n = k + 1

terse dagger
#

right so you assume it works for k

torn dome
#

yeah

terse dagger
#

so now you go look at $11^{k + 2} + 12^{2(k + 1) - 1}$

soft zealotBOT
#

Katharine

terse dagger
#

You wanna transform this into some shape such that you can use your assumption

torn dome
soft zealotBOT
#

Sean [Ping On Reply Please!]

torn dome
#

how to use this

#

to 'transform'

#

ik that i gotta add and subtract smth

#

should i do $11.11^{k+1}+12.12^{2k-1}$

terse dagger
#

what you can do is use the binomial theorem

soft zealotBOT
#

Sean [Ping On Reply Please!]

obtuse hedge
#

Are you sure about the 12

torn dome
#

yea ig

#

did i make a mistake

obtuse hedge
#

Check the exponents

torn dome
#

yea

#

mb

obtuse hedge
#

(When you take out 1 twelve, the power should decrease by 1)

torn dome
#

alr i solved it

#

i had to add and subtract $11.12^{2k-1}$

soft zealotBOT
#

Sean [Ping On Reply Please!]

torn dome
#

ty guys

#

.close

final saddleBOT
#
Channel closed

Closed by @torn dome

Use .reopen if this was a mistake.

obtuse hedge
final saddleBOT
#
Available help channel!

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Remember:
Ask your math question in a clear, concise manner.
Show your work, and if possible, explain where you are stuck.
Do not immediately ping people or roles. After 15 minutes, feel free to ping <@&286206848099549185> once.
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Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.

terse moat
#

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

next thorn
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I think that sufficies similiarty.

terse moat
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oh so you only need to share the length and them both being right triangles? :O

obtuse hedge
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🤔 no you need one other angle to show it as well, otherwise a bunch of triangles are similar

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(Which is easily shown since the big triangle is similar to them both)

terse moat
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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

terse moat
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oh and this exercise is from khan academy

obtuse hedge
terse moat
next thorn
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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!

terse moat
next thorn
terse moat
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omg you are right! :O

terse moat
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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)

next thorn
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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

next thorn
terse moat
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makes a lot of sense, I think like I can understand and prove similarities based on angles a lot better now

terse moat
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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 ,-,

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thank you, how do I mark this as solved?

next thorn
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you type .close

terse moat
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.close

final saddleBOT
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next thorn
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BEST OF LUCK

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YOU CAN DEF DO THIS!!!

terse moat
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maybe someday I will be able to help people out here too

next thorn
terse moat
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terse moat
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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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signal cipher
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steep nest
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because the outside part of the shape has a higher rotational distance than the cone part

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the part with a large area of the cone moves less distance than the large area of the cylinder

signal cipher
steep nest
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well just look at the 2d image you posted

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the ratio between the areas is 1/2 right

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half

signal cipher
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yea

steep nest
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now if we rotate it along the line, you see how the inside becomes a cone

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and the outisde becomes a cylinder, without the cone?

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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.

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Try to visualize this

signal cipher
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what i was thinking

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is that the ratio would stay consistent

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in every rotation frame

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so when the 3d shapes are form how does the overall ratio change

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ohhh

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i get it

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overlap

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ohh

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is overlap right reasoning?

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.close

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restive sinew
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restive sinew
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how do I solve it?

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income=exp+saving

tired walrus
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incomes are 2x and 3x, expenses are 16y and 21y, savings are 4z and 9z, and 4z+9z = 312000/12

thorny otter
iron basalt
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The answer is Rs 60000 per month

tired walrus
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tired walrus
iron basalt
tired walrus
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read what the bot said

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don't give out answers

thorny otter
tired walrus
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312K is the annual savings of the two people combined

iron basalt
tired walrus
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ok sure. good for you.

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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

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@restive sinew you here?

iron basalt
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I think he's gone

final saddleBOT
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@restive sinew Has your question been resolved?

restive sinew
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z=26000

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rest is easy

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.close

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restive sinew
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restive sinew
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How do I start it?

leaden moon
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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

soft zealotBOT
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1 divided by 0 equals Infinity

leaden moon
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i think this requires a system of equation

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let the time $A$ makes through the distance as $x$ and the speed $A$'s going is $y$

soft zealotBOT
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1 divided by 0 equals Infinity

leaden moon
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so the distance we need to find is $xy$

soft zealotBOT
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1 divided by 0 equals Infinity

leaden moon
desert mantle
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generally speaking, a good first idea is always to give names to all values

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and then try to find some equations connecting them

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@restive sinew Has your question been resolved?

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@restive sinew Has your question been resolved?

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@restive sinew Has your question been resolved?

tired walrus
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op is not showing any signs of life

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old quarry
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old quarry
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AB: 3y-2x-5 = 0

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AB distance = sqrt(13)

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i took a point P (x,y)

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distance of P from line. =
d=|2x1-3y1+5|/sqrt(13)

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area = 1/2 x (2x1-3y1+5)/sqrt(13) x sqrt(13) = 10
2x1-3y1+5 =20
2x1-3y1 = 15

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a=2 b=-3

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which gives me ans 4

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which is in the options but is wrong

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where did i go wrong

left echo
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What the hell is that font size

old quarry
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sorry its from some website

floral zenith
old quarry
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oh ye the modulus

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ok but how to decide if it opens positive or negative?

fossil kiln
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Also u gotta use the fact tht P is above line AB

old quarry
left echo
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If P is above the line then putting it into the line's equation will be positive

floral zenith
old quarry
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ohh alr alr fine

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thanks

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.close

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fossil kiln
old quarry