#precalculus
1 messages · Page 71 of 1
I see
yeaaaaaaaaaaaaaaaaaaaaaaahhhhhhhh
I'd show you the solution except it would ruin the satisfaction of doing this yourself when you're done with limits and can execute things quickly
My question is nothing compared to this!💀
Well you're just starting
Yeah!
Yes in my JEE class
I have learnt that in my normal 11th
Oh hsc?
yeah
Same
My instructor was hella surprised when i started spitting lhospital to derive standard limits
Bro was like stop, lhospitals is a weakness

And until recently i didnt understand how true that was
really? just recently?
But now im stuck in my stubborn habits and i cant change how i do things

but you do know other approach right?
Yes i spammed lhospitals for mains but when i started doing adv prep a few months after completion of my course i got so many roadblocks
two is plenty to this
Ik theres some stuff like taylors as well but idk shit abt that
Will learn in college prolly


Also keep in mind that series expansion is a very powerful weapon
Just learn it for sin cos and ln and you're set
yeah I haven't tried to use that rest of my life till now
Another thing i ignored applying due to lopital spam
But now ik its easier and i do it occasionally
Not really been solving limits much tho recently, mostly indef integ
spamming l hop?
The real question is why am i doing math daily in my vacation 
doing math in vacation lol?
Like ngl ive been in this server four days and
It may please minds of mathematicians lol
💀
i have 768k messages and have been in this server for 8.5 years, calculate my rate of messages per day.
Tho tbf most of it is easier since i usually only pick those i can answer acchese so i can help the asker
if you need an exact start date: january 15, 2017

,w 76810^3/(8.5360)
247
I aint doing that shi bruv 
please don't call me "brother" or any variation thereof.
you called me "bruv" just now and i told you not to do that.
Ok soz soz
How long you been here though?
march 18 2024, now calculate
For her messages or yours?
monkey d luffy joined at that day
I'm assuming you expected me to do the division right 
What why did he say 2024 then lol
How bruh!?
eventhough only 4000 msgs lol
but you lol executor
Fr
yes(I ain't an active boi anyways)
I will come sometimes to help
sometimes to get help
Well i have nothing to do rn except do coding math and games
sometime to chill
So im here a lot
Vacations are pog
When are you going to get busy again? lol
anyways enjoy your vacation prolly
But its fine ive been on holiday for 20 days already
Tyty
and watch one piece in this month
lol
Why does everybody tell me to watch one piece its a thousand episodes 
The longest anime ive watched is naruto
everybody? lol
You won't regret watching it
Ive watched like 50+ anime till now nothing is close to 1000 episodes
Ok i might try
Rn I'm watching peaky blinders tho
I have watched a single anime with a range of 1132 ep
Thomas shelby 
I'm assuming that's one piece? Or something else??
not only that though
yea
You've watched?
yea
O means oh

lol
literally me
I started watching it
Disappointment in 2 episodes
I haven't touched it
Just what is that shit
I instantly left
you won't regret even a single ep in op i tell
you will die in oda's foreshadowing lol
lol
Alr cool
Allen app??
yeah howdya know?
Me allen too lol
This wasnt so developed in my education period tho we just did things on whatsapp and offline
Good to know theyve integrated some stuff
Oh you go to a real school?
to keep up
are you integrated school?
Dw it's the same for offline people 
Yeah
Hard to do real school exam though
But i concentrated so it was easy
Got 197/200 in cs so that just clutched big time

Till what time real school
3 for now as it is started just now and original till 6
what is this btw?
O so school close to home
Never sacrifice sleep tho btw
takes 6.15 to reach
Do you?
sorry(idk hindi)
I tried for 2 weeks during jee
oh i see
You're nri?
you did? lol
Did not work
non-residental indian??
Or might just be from south or north lol
south lol
Yeah
I see
I speak kannada
ohh good i speak tamil lol
Ooh my future college might be in chennai
Still thinking tho not decided
lol 
yeah we may die here
Just realised 
ping me
when you check someone's profile, it tells when they joined the server below 'about me' part
and i will
you if you talk here now, if you wanna say something to me, ping me in #chill
Hey @wraith escarp sorry to bother you, but is this a corner?
yes
there are two different slopes at that point, aka the derivative is discontinuous
gotcha, so with my corners being here:
Where/what exactly is my slope? or point i place for f'()
there is a jump in f'(x)
itll be f'(x) = 0 until -1, then start being f(-x) = -1 after that
im confused on how to graph that on f'
Like this?
a) the slope isnt -2 for the downward part of the graph
b) there should be another jump at x = 3 since f(x) starts going up
?
not correct past x = 3
so at 4?
whats the slope at x = 4 and whats it at x = 5?
does it change?
if not, why does your f'(x) change
also, speaking of which, what is the slope of f(x) at x = 4?
i doesnt change and the slope at x= 4 is 1
then why is f'(4) = 0
you are making random lines
the slope at x=4 is 1 as you mentioned
therefore f'(4) should be 1
you arent trying to make the slope of f'(x) match the slope of f(x)
the actual y value of f'(x) is the slope
f'(x) should contain (4, 1) because the slope of f(4) is 1
it should also contain (5, 1) for the same reasons
whats the slope at x = 3.5
nothing so i have to make it go to the 3
what do you mean nothing?
well theres no line there i jumps from 3 to 4 so shouldnt it be
yeah this one is right
the slope at x = 3.5 is also 1
and your new correct answer does in fact have (3.5, 1) so its looking good
so can you walk me through the steps again
i mean your answer is right, do you have questions about specific parts of it?
ie why some things are how they are or how we got something specific?
im just confused why we used straight lines for everything even though after the dashes it goes up
well
"it goes up" is the misunderstanding
the function does go up, but the slope doesn't
x = 0, 1, 2 all have the same slope
it doesnt "go down"
any tips on memorizing very long formulas for someone with weak memory? 🥀
you shouldn't be in a situation where you need to memorize very long formulas
what about college entrance exams
Which one for example?
yeah can you show the long formulas you're finding yourself having to memorize
here
.
hm
well, this formula's written in a rather unwieldy way, but if you aren't familiar with sigma-notation it might be a bit unavoidable.
though again i would advise AGAINST memorizing it into a thousand fragile pieces
and instead learning about binomial expansions in depth
just learn how the formula is derived, and then you will learn the formula, because, you know how it was created, and how it works. You shouldn't just mug up. Anyways it is your choice
it's also not very hard to memorize
like you should see the pattern in binomial expansion formula
i think that the longest formula worth "memorizing" is the law of cosines
true
for me personally it's worth deriving
I'm still on my quest to get used to it by deriving
i didn't say you should memorize it blind
its derivation is pretty important to know
but at the same time, when you're practicing with it, thinking about the derivation every single time gets taxing
I'll raise you the quadratic formula.
about the same length innit
$c^2 = a^2 + b^2 - 2ab \cos(C)$
or maybe
$\cos(C) = \frac{a^2+b^2-c^2}{2ab}$
vs.
$x = \frac{-b\pm\sqrt{b^2-4ac}}{2a}$
Ann
Hmmm, the quadratic formula feels more involved to me ... but I acknowledge that is not an exact science.
(Ironically, I can remember the quadratic formula, but I need to look up the law of cosines).
I think it is much easier to remember the law of cosines in the 1st form as it can be easily seen that Pythagoras theorem is just a special case of law of cosines.
yeah i was just giving both forms to make a comparison on complexity/perceived "length"
what about cos(x+y)?
Is that worth memorizing, though?
yes imo it is
Yeah
Every formula is worth memorizing if it saves your time
Hmm, at least I've never bothered. If I need it, I'll either look it up, or derive it from e^it.
Only do it if you know how to get them at any moment
if you're a school kid who has not yet learned about C then it's a bit of a no go
(we don`t talk about fermats last theorem)
pq-formel, next
<@&268886789983436800> spa
spam
Moderators Need A Spa Day
What is that?
oh I keep forgetting you're not German
here ya go
ya filthy American
if you have x^2 + px + q, so you just need to divide b and c by a
I'm not American either.
ah
lol
what do quadratic function do with geometry formula?
behold the final boss of basic geometry, superior Menelaus's formula
I mean basically this is harder to memorise than any formula
BP × AM/MB = AN/NC × PC
idk why I feel this is easier to remember
oh that reveals a possible proof right
triangles APN and NPC are related by scaling
and so are triangles AMP and BMP
ngl Idk how does that reveal any proof but I really meant I only feel like writing the same equation like that is easier to memorize, not like I know how to prove the equation

no
its quite easy to memorize if you solve problems with it
just use Thales omg
how is Thales related?
if you take P at infinity, it becomes thales theorem
oop- ah
the name is so shit, cause it could also refer to right angle inside a circle
anyone?
I would love to help but i can't read english handwritings.
From what i can read you calculated: (1+m/8x)^(1/3) = (1+m/24) ?
Correct me if i'm wrong or they're symbols i don't know about
,, \sum(ab)=\sum(a)\sum(b)?
Monkey•D•Luffy
Yes
Binomial approximationn
not in the slightest
does not even work for sums 2 terms long 💀
$\sum(ab)=\int a(x) dx*\int b(x)dx$
Trust me bro
Enterlessguy
But thank you for this bro 
well I was assuming you were using sequences for a and b
So just let the sequences be defined for R instead of N
Trust trust
for the record, i will be a killjoy on purpose and say that @drifting oyster's thing is completely false and also nonsensical.
Thank you, ann. I literally thought that is true lmao
ok yeah this sort of naïveté is exactly why a space like this needs to be free of falsehoods stated so brazenly as @drifting oyster did
I thought it is true since sum and integral has some relations to each other
I thought It is super helpful
but so sadly it is not true
for my unfortune
lmao
Also @modest bolt Do you know the relation b\w sum and int?
Are you writing the relation????
If yes, nvm me lmao
Hell you really did write the relation
int is just infinite summation of smaall x but you can know better by google
You should understand reln betn integral and sum by looking at the example of an area under the curve problem
i am talking about basic definition of integral which we learn to find area under curve, idk any other relation if there is
You make infinite small rectangles and add all their areas together to get the area of the curve, which is the integral of the curve
there are good animation vedios to explain that, you can watch if you want
Yeah
i know there is a formula for this
why does this not work
it works for one but there is another
What if the difference is 7pi/12 instead
my number is right but their is another soultion
Does what I said not apply?
wouldn't it get picked up by the mod
What
That tells you if this angle is 5pi/12 (absolute difference between the two angles with the x axis is the indicated angle by exterior angle theorem)
But my point is that this angle could also be 7pi/12
Because then the acute angle would be pi-7pi/12=5pi/12
@gray magnet Hello?
yeah your right
i forgot that arctan only gooes anticlockwise
i though it would account for this
i know its not in english
but why is that the k is going to n-1?
shouldn't it be both k=0 to n?
can someone please explain why the null set is a subset of all the other non-empty sets...I mean the null set doesn't contain any element of another Set.
I think its so that you dont get a second a_n*b_n term that you already got from the first term
ahhh
hey
im learing deriviatives rn
i like calculus its very fun
what can i expetc next
academic suffer and Frustration
nice!
tfw you realize 1/x looks the exact same as 1/y
more derivatives, and antiderivatives, and going back to limits again, and then back to derivatives, oh and you remember that math trick you forgot from middle school? yeah you're gonna use that again, but only for a week.
✨ m. a. t. h. ✨
can anyone tell me the definitions of tangent lines, cause it seems like its really useless and rendundant to me
from what i know Tangent line is a point in a curve that sort of like kisses the point that from the lines itself it goes forever, but then Why do we need all of this fancy Formula and others just to decide that one point
and what is actually the use case of this tangent line?
it is a line that touches a curve at exactly one point
it is used to calculate the slope of a curve at a certain point
the slope?
isnt tangent line return a line equations
rather then a slope
cuz if u want a slope u can just use the point slope formula for it
wdym “that math trick u forgot from middle school”
Nope
I don’t know if this is an accepted definition, I haven’t seen it before, but it’s something I thought of. A line say l(x) is tangent to a curve say f(x) at a point say x = a if l(a) = f(a) and there exists an open interval I containing a such that l(x) >= f(x) for all x in I or l(x) <= f(x) for all x in I
if this is wrong, please let me know but I think this works?
I think there are subtle differences with this and the calculus definition I believe
what do u think? @solar dagger
hmm so in short it is like uhm a line that Goes to the point x =/> or basically shows the direction
but while solving the tangent line problem itself we can know the Slope of it as we most of the time
will need to find the slope first
idk what u mean?
like line a goes to line x?
there’s no line a and line x idk what u mean
then wdym?
No I don’t know what u mean
why
idk what this mean either lel
if im wrong and u dont know what i mean then i dont know what that mean either.
A tangent line can intersect a curve again, further away
I think what I said is (hopefully) very clear. which part don’t u get though?
all of it honestly.
oh right
then take more time to think about it
but i think i already got the definitions of tangent line it self, just finished doing some research
what is it then
its basically a Direction from point a to be point b
it's the unique line that passes through (a, f(a)) and where the slope at x = a is f'(a)
given a function f and a particular x-value x = a
what is (a, f(a)?
it's a point's coordinates
is what I said fine btw? Is there a reason what I said isn’t used more often? I feel like it’s simpler at least to understand intuitively
yeah that's a plausible real analysis definition but their ability isn't there yet
it should be fine, its just harder to understand smt like that, i cant understand it at all though.
when you start using open intervals you'll have lost them already
oh u can use function for a point coordinate?
yeah!
x-coordinate = a
y-coordinate = f(a)
I haven’t done real analysis
woah i just knew that
but why u use function?
is there any special reason on that?
it's better to think of a line in terms of a point (the 0th derivative) and the first derivative
also tangent line always return a line equations right not a slope? correct me if im wrong.
this definition is perfectly fine locally
it's just not phrased in the language of calculus
that's moreso a geometry definition
wait it’s not though
uhm what is 0th derivative and first derivative? do u mean the point?
yeah, a tangent line is a line
oh yeah you don't know about Taylor series
i see oke oke.
yeah not yet
Taylor series talk about the best polynomial approximations to a function centered at a given point
a lot of functions like sine and cosine, or e^x aren't polynomials
function centered?
what is that?
the function exactly matches at that particular point
also if u dont mind can u tell me the basic about taylor series, i heard it was very beautiful and fun
as you move away, to the left and to the right, the approximation gets less accurate
havent learn about it at all though
so like 0,0?
Taylor polynomials are incredibly powerful for approximations and analysis.
Help fund future projects: https://www.patreon.com/3blue1brown
An equally valuable form of support is to simply share some of the videos.
Special thanks to these supporters: http://3b1b.co/lessons/taylor-series#thanks
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Full series: ...
yeah! that's a common Taylor series
we approximate the function at x = 0
😮
alright alright lets talk about the taylor later
will watch it soon
also back to the Tangent line
ok
usually the formula for tangent line is what? i asked ai and it says it was the point slope formula
im not sure if that is right though
lets say a circle
yes that's correct
i want to find a tangent line of a circle, did the formula will be different for like a Box/triangle.
yes
Oh?
I know what’s it’s trying to say, but the locally part makes it weird. Like how are these two different
do u mind tell me about the formula?
a local approximation follows epsilon-delta, so it must have the same slope at the point of tangency
waat there is two thing? the thing that crosses and touches?
i thought its only touch
yeah, so the left image is tangent at one point
it is a tangent line where it says 'touches here'
what do you want to know
south what’s that pfp btw
woah oke uhm this going to be pretty long conversation, cuz i always ask things too much most of the time.
soo like lets say i want to find a Circle tangent line, how can i do that?
the tricky bit is finding the slope at any point on the circle
http://www.rootmath.org | calculus 1
We take the derivative of the equation of a circle.
watch this it'll teach you how
a circle is very nice actually
if u remember geometry
yeah that's another approach, by similar triangles
what kind of geometry?
i remember circle formula like pi and sort
The line from the center to the point of tangency is perpendicular to the line tangent to the circle at a particular point
@willow skiff
It doesn’t matter
it's a local landmark of the jetty here
yeah
ohh then yes i do know, i actually just learned it yesterday

gtg now, need to wathc the video rq
then ill get back to here
but this approach just uses geometry
you don't need any equations to realise that
you can show it using calculus, so calculus always works no matter the shape
but then that's a bit overkill if you only want to know for circles
where’s here
Aus
eg the slope of the radius is 5/3 so the slope of the tangent line is -3/5
Oh cool
@willow skiff
just finished watched it, btw what is the different between Calculus method and geometric method on finding the tangent lines of a circle?
did calculus more accurate or what is the different?
the difference is in how you find the slope, so finding f'(a)
but the result will stays the same?
once you find f'(a) you can just sub into $y - f(a) = f'(a) (x - a)$
south
yes
i see yeah i think ill stick with geometric for now, until i understand calculus more
also what about if like a Box?
yeah i didn't realise you just wanted the circle
I don't get what you mean by a box
a curve mb, like an oscilating curve
up and down
or quadratic curve
or cubic curve
okay for all those ones you need calculus
oh why is that?
calculus is the most general method
all of them
it's based on finding the slope of the line as you bring two points closer and closer together
when those two points are the exact same, that limiting slope gives you the slope of any curve
it seems hella pointless at first, but it'll keep coming back up over and over again throughout calc.
ohhh i see
and it'll be easier each time
yeah sure ill learn it
for circles we use the fact that the tangent and radius angle is 90 degrees
that's only for circles
yeah it is indeed kinda pointless until i realize the use-case in calculus
there's a few other classes of functions where you don't need calculus, excluding lines
then i need to learn about derivative first am i right?
or wrong
but then you'd have to be smart to think of how you could do it without calculus
start with limits
and this is really all it is. it's simpler than it seems at first... it really is just a line that uniquely touches this particular spot. this whole thing will make more sense when you get into derivatives and the like.
yeah it's a natural extension of point slope form
you literally replace m with the derivative at x = a
that's it
uhmmm, what is this mean if u mind to elaborate it?
only true for a circle
so its perpendicular
woooooooahhh but i still got question about circle since u talking about circle
circles are triangles and triangles are harmonic swings and harmonic swings are vibrations and everything is everything
QED ⬛
in circle geometric formula there is an extra (x - h) and (y-k)
and why is that? i mean the rest its similar to the standard form of Circle just with extra (x - h) and (y - k) also when i calc it, it seems like used for multiplication kind of thing but i believe there is a deeper Meaning in it.
yeah circle and triangles is soo related idk why.
hehehehehehehehehe
like the unit circle uses triangles for the circle
reasons. lol, the short version is "because, universe"
lol i mean that is true but
whatcha mean "extra"?
maths guy always ask for a reason and prove.
Are you talking about the -h and the -k?
(x₁ - h)(x - h) + (y₁ - k)(y - k) = r² this is Geometric formula to find the tangent line of circle
(x - h)² + (y - k)² = r²
and this is for the circle standard form itself
it looks pretty similar except for the
extra (x-h) and (y-k)
the difference is....
one has an x and an x_1 <--- one is symbolic, one is defined
the other has two x <--- both are symbolic
yes i know that but
it's the same formula, but you're picking points for the tangent line, so you take up two of the coordinates
lol, I should be more careful with my words.
hmmm
it's to do with function transformations
i think this is right
$x \mapsto x - h$ moves the function $h$ units to the right
They're the same, as in, the tangent line equation is derived from the original equation
south
ait wait
dont use that kind of explanation i beg u
i wouldnt understand it at all lol.
then you need to go back and revise
revise what thing?
havent learn that at all ngl.
i think i get u
let me think rq
Now that we know the basics regarding graphing algebraic functions, it's time to learn some tricks that will come in handy as we graph different kinds of functions. Specifically, there are terms inside functions that do very predictable things to graphs, and if we learn what these are, we can look at certain functions and quickly graph them with...
ohh that is right @rough arrow
such as, if a known point on the circle is (5,2) then x1=5 and y1=2
so
(5-h)(x-h)+(2-k)(y-k)=r^2
you have gaps in your knowledge, cause you're self-studying or something right
you can't start calculus without having a deep understanding of functions
the x_1 and y_1 is uses for the tangent coordinate
ohh this, i have learned it before
yes im self-studying.
here's another example of what I mean
do you have a textbook you're following?
yep yep yep!
another fun one to realize... point-slope form? y-y1=m(x-x1)... that's 100% equivalent to y=mx+b, just written out so we can recognize exact points in the formula, which is therefore easier to create tangent lines
just youtube i dont have that kind of textbook unfortuntately
Check out something like OpenStax for a free textbook!
My school uses this book for our course 🙂 and it has practice software in it, too!
yeah so now i just need to know the reason behind it, by learning function transformation.
James Stewart's Precalculus for example
Desmos has free(?) lessons and calculator toys too
oh wow
yeah even if you follow Khan Academy you won't be that far off
at least it's organised and there's quizzes on every subtopic
and you get energy and plants and superpowers and stuff, lol
YouTube is good but it's not a replacement for an actual curriculum
honestly my learning pattern is not organizied at all
I love Khan but I don't use it consistently enough hahaha
I do think you shouldn't stress about if you're "ahead" or "behind" or not
i often jump from another to another and yet i still understand it. but at a different concept like this im loss
but if you try structuring your learning you'll find maths becomes easier
it might sounds abit funny that i know trig but not function transformation fully
so yeah i guess ill try
you know a sin(b(x - c)) + d?
do u have any tips on this?
yeah
you know what the a, b, c, d do?
literally just work through one chapter of this book
for vertical shift
see how you go
great, so you do know
this is for precalc right?
but you haven't realised that it's the same for all functions
yep
yes Lol, math is actually really fun and myterious for me.
aight
wow the website is actually full of e-book about math thanks @rough arrow
alright last thing before i go and read some books, for a structured learning do u suggest me to Read a single book at the time until i finished it
or something else?
the reason is because of math, lol. i apologize if my descriptions are hella basic right now... i'm super tired, but here's why:
if we know a number is, say, 5, but we want to find a spot where it equals 3... we do math.
- 5-3=2, hey dope, we found a 3 in there!
but what if we're dealing with x & y at the same time?
well, same thing applies. use point-slope form. (I can't think of a good example right now... too sleepy, but I hope this shows how it's more simple than it seems)
lol i keep falling behind in the convo lollllllllllllllll
probably just work one chapter at a time
you can browse multiple books to see which one explains the best as well
main thing is just read and practice
if anything is unclear watch YT
but try to follow the book if you can
I'll add that I'm taking Calc 2 this summer, and the nice thing about Algebra, Pre-Calc/Trig, Calc 1, 2, 3... they all just build off each other.
yeah math is got alot alot of abstraction someetimes its just like really intresting and annoying to find the reason on why this happend or this happend because usually at school we only teached to remember something and the teacher doesnt even tell us the reason behind it, also you are right in every math formula there is alot lot lot of possiblity going on like a number 5 and 3 can become a coordinate or it can become this and bla bla bla.
sometimes linearly... one chapter builds to the next chapter
yeah literally don't look at anything before precalc
there's a lot of repetition
you don't need to look at alg 1 or alg 2 if you learn precalc properly
btw precalc is just about the basic of calculus right?
it's "essential maths before starting calculus"
other times in spirals... you'll learn a trick, put it on your reference card, then not use it for a while until you remember it exists when you're stumped 3 chapters from now
got it!
hence my joke earlier about "remember that math trick you learned in middle school?"
because really, math curriculum really just goes in spirals, endlessly 😆
if you're self-studying you don't follow what your school or your teacher is doing, by definition
you can go at your own pace
also a lot of schools have mandatory hours for learning mathematics and teachers need to find a way to fill up the time somehow
exactly
"hey, i know you're in the middle of some complex integration, but did you forget how fractions work?" <-- happens more often than you'd think, hahahahaha
about the spiral anology, which is very very useful and it's true
alright i gtg now guys, really glad that i meet you two, i learned alot today about how to learn and this tangent line.
thank you : )
after you learn precalc then you'll find that calculus uses precalc a lot, obviously
so you can revise precalc and learn calc at the same time
main thing is try to learn it well right now
90% of all calculus mistakes are caused by not understanding precalc
some of the precalc lessons are secretly teaching you calc... then you get to calc and learn it for real and go "hey waitaminute, this looks familiar!!!"
Yello have a quick question, hopefully not interrupting anything
If I took precal dual this year, could I js take the precal AP test next year w/o taking the class
I feel like the class would lwk be the same, I only would have to study the frqs?
yes, that's correct
oh lol yeah, that's how AP stuff works.
when you take the test, don't be me and forget to write down the time
I'm also take AP calc ab this coming school year
there's not really a 'how'
lol, i showed up to math period and was like "where is everyone?"... teacher said "lol, the test was like 5 hours ago man, you missed it"
I will say practice with the formula booklet and underline the key bits of the question
Why $\sum_{k=1}^{\infty}\frac{1}{k^2}$ converges to 2 while $\sum_{k=1}^{\infty}\frac 1k$ diverges?
Monkey•D•Luffy
oh my bad
I thought it is 2
,, \sum_{k=1}^{\infty}\left(\frac{1}{2^k}\right)
Monkey•D•Luffy
this @uncut mulch
that will be 2, yes
Is there integral approach to this?
basic integral approach allows you to show that the sum is less than 2
getting the value of pi^2/6 is more complex,
(Basel problem)
I see
also this is more interesting that $\lim_{n \to \infty}\sum_{k=1}^{\infty}\frac{1}{k^n}=1$
Monkey•D•Luffy
complex even to you?
or me?
not for raijin
raijin? lol
how?
oh yeah like under the definition I had y = |x| would be differentiable at x = 0
yeah you just assumed differentiability
it happens
that's why these hidden assumptions (incl continuity) are super important
sorry wdym?
It just seems like it’s a kinda different definition, I’m not sure if that necessarily makes it wrong per say, but I’m not really sure
another problem is that you can have a function which is differentiable but crosses its tangent line infinitely many times in any open neighborhood of the point of tangency, e.g. x^2 sin(1/x)
ah I forgot about that
ohhh thank you for that
It does have a tangent nevertheless 
also u can’t rlly do calculation (or at least it’s pretty tedious) with the definition I had, is that also why it wouldn’t rlly be used?
a simpler but more fixable issue is tangent lines at points of inflection, which are above the function in one direction and below it in the other
but i think that the definitions are at least equivalent for twice-differentiable functions whose second derivative has constant sign in some open interval of the point of tangency
ohh yeah that is definitely a problem. how could u amend the definition though for that?
i had the idea of allowing it to be above on one side and below on the other, but upon closer thought that would clearly allow lines which just cross without tangency, so i'm not really sure
It does feel kinda odd like geometrically for sin(x) to have a tangent line at x = 0. I don’t think there’s a way to fix it then
like if u r using the “touch but doesn’t cross locally” definition
yeah. i think that the "touch but don't cross" notion seems to be a way of trying to enforce "pointing in the same direction" without explicitly invoking that notion, but the more we dig into it the less those seem to line up
wdym “those seem to line up”
I think what I had is equivalent to the touch but don’t cross but yeah there are differences with the calc definition
as in, touch but don't cross and the ordinary derivative definition (which attempts to directly formalize "pointing in the same direction") seem to match less under scrutiny
I think both are formalized. I think they have different ideas of course
Is $\frac{\sin x}{x}=\prod_{k=1}^{\infty}\left(1- \frac{x^2}{(k\pi)^2}\right)$?
Monkey•D•Luffy
yes
Is $\prod(ab)=\prod(a)\prod(b)$? @willow bear
Monkey•D•Luffy
Which part of it is horrible?I mean correct me
how to perfectly write it
i mean $\prod (a)$ is... vague
Ann
i would have rather seen you write something like
$\prod_{k=1}^n (a_kb_k) = \prod_{k=1}^n a_k \cdot \prod_{k=1}^n b_k$
Ann
wdym
Do we should take extra care to infinite products? @willow bear
you should exercise extra care when dealing with infinite anything
not just products
may it be trickier than normal
I see
is there anything trickier about infinite products rather than sums?
@whole void Which grade are you?
11
,, \prod_{k=1}^{\infty}{\frac{(k+2)(k-1)}{k(k+1)}}=\frac{\prod_{k=1}^{\infty}(k+2)\prod_{k=1}^{\infty}(k-1)}{\prod_{k=1}^{\infty}k\prod_{k=1}^{\infty}(k+1)}
Monkey•D•Luffy
Can this be true? @willow bear
no, $\frac{\infty}{\infty}$ is a bad idea
Ann
,, \prod_{k=1}^{\infty}{\frac{(k+2)(k-1)}{k(k+1)}}=\frac{\prod_{k=1}^{\infty}(k+2)\prod_{k=1}^{\infty}(k-1)}{\prod_{k=1}^{\infty}k\prod_{k=1}^{\infty}(k+1)}=\frac{k-1}{k+1}?
Monkey•D•Luffy
ok no that's just very wrong
Is there any way to approach this?
what, to calculate this infinite product?
yep!
Just the approach is enough
I like every math stuff(cause I am an iron man lol)
but i would look at the n'th partial product of that thing (ie instead of taking all the terms to infinity, look at the product of just the first n terms) and then cook up some magic with stirling's approximation formula
or whatever else is appropriate
maybe you won't even need stirling
maybe it can be done with just careful factorial bashing
It telescopes tbf (assuming you meant to start from 2 instead of 1)
that it might
,, \prod_{k=1}^{\infty}{\frac{(k+2)(k-1)}{k(k+1)}}=\lim_{n \to \infty}\prod_{k=1}^{n}(1-\frac{1}{^{k+1}C_{2}})?
Monkey•D•Luffy
may be correct but i don't think it's helpful
Did you mean to start from k=1 b/c the term for k=1 is equal to zero
Yes exactly
sorry for the mistake
Yeah idk how this would be helpful for a telescope then
I got this prod from that comb lmao
Idk how to telescope it @raw hill
it is confusing
Π(k=1→n) k = n!
Π(k=1→n) (k+2)(k-1)/k(k+1)
= (n+2)!(n-1)!/n!(n+1)!
= (n+2)/n
= 1+2/n

idk if its correct or not
but looks correct
The product is zero for starting at k=1
Starting at k=2, it’s (n+2)/(3n)
oh
$\prod^{\infty}_{k=2} \frac{(k+2)(k-1)}{k(k+1)}$
Civil Service Pigeon
What id do here is notice that (k+2) and (k+1) differ by 1
As do (k-1) and k
So that’s where we’ll get the most “immediate” cancellation
You may not see what I mean rn, but it’ll make sense later
Because of this, I’d split the product up as follows: $$\prod^{n}{k=2} \frac{k+2}{k+1} \cdot \prod^{n}{k=2} \frac{k-1}{k}$$
Civil Service Pigeon
Now, try writing out the first few terms of each of these products
And see what you notice
@hoary iris
Can we separate like this @raw hill
but can't for division
Division is just multiplying by the reciprocal so …
$\prod a_k b_k=(\prod a_k)(\prod b_k)$ as long as everything is well defined
Civil Service Pigeon
Which should be easy to see
.
I see
Ex. This infinite product is 1/3 (which I’ll let you work out later)
But $\prod^{\infty}_{k=2} \frac{k+1}{k^2}$ is zero
Civil Service Pigeon
But by splitting the infinite product as you did, they’re indistinguishable
This is why you generally do what Ann mentioned here with partial products/sums/…
Then take the limit
This way you don’t run into issues with orders of infinity in the middle of your process
What is partial products/sums?
Basically what I did here
Find the general formula of the product up to the nth term
uh
oh wait finite ones
mb
was about to say shit diverges
I'll try this and let you know(If I got it or not)
k
one min or two min
what are you trying to do here? @hoary iris
Probably what I just said (?)
Find the partial product by telescoping and then take the limit
trying to find that infinite prod

why making it hard, you can simply expand and see all terms cancel out and you left with 1/3
,, \frac{n+2}{3n}
Idu
@raw hill
I think I am done
@modest bolt Tell your idea btw
That’s what I was going for with having them write out each product and observe the cancellation
Also so we can highlight the idea of taking the limit of a partial product to get an infinite product
Also I was breaking it down because
Yk they’re new to this
Should be (n+2), not (n+1) in the numerator
this is working! isn't it?
I don’t know what that’s supposed to show
Monkey•D•Luffy
And now to find the infinite product, we can take the limit of this as n goes to infinity
@hoary iris
What is that limit
from there i understand
1/3

,, \prod_{k=2}^{\infty}{\frac{(k+2)(k-1)}{k(k+1)}}=\frac{\prod_{k=2}^{\infty}(k+2)\prod_{k=2}^{\infty}(k-1)}{\prod_{k=2}^{\infty}k\prod_{k=2}^{\infty}(k+1)}=\frac{2-1}{2+1}
It does work
right?
For the reasons I said earlier, this is very abusive
But if you want to write this as informal scratch work that isn’t meant to be read
Go ahead
It is very hard to read but applicable
right?
Monkey•D•Luffy
which is 1/3
pigeoooooooooooon
@raw hill sorry for pinging you repeatedly
@modest bolt What are you typing so hard and didn't even sending?
again, infinity/infinity is abusive
If you want to write it as scratch work, go ahead
But I’m not going to continue parroting back the same answer to you
I see
Probably writing out their own method but it takes longer to write then it’s not in latex (I’m assuming this since their last msg also wasn’t in latex)
Probably going to be with factorials based on what they sent earlier
Which is fundamentally the same thing
You just “bunch” all the terms together before cancelling
ye
anyways, we can bunch the terms and cancel it in scractch work
there my problem done lmao
Thank you for you help! @raw hill and @willow bear
shubham I'll wait for your idea
ping me once you're done
Π(k=m→n) (k+l) = (n+l)!/(m+l-1)!
Π(k=2→n) (k+2) = (n+2)!/(2+2-1)! = (n+2)!/3!
You can rewrite others like this and see the whole product= (n+2)/3n

I want to say you something bro
You have a great ideas to explain
please latex them bruh
wsp
gpt??
Happy sad journey here!
Nah I HIGHkey like maths
Everyone does that before coming here lmao
I'm 12 btw, so no weird shi 🙏
uhhh
you're not allowed to be on discord if you're under 13, sorry mate
I am 13 in 2 weeks?
ban him lol
- WEEKS
dunno this is up to the mods

I just joined 😭
You'll be muted for 2 weeks lmao
are we deadess
fu-
yes it was:
pi^2
sorry, we can’t have you if you’re under 13
they’ll be allowed to rejoin after 2 weeks.
Ok, Thank you!
What a strict rule lol?
I wanna test him with integrals
btw
it’s discord’s TOS
so sed
I can see You forced gpt to get this result Lmao
after series of wrong results
it is i just pasted the latex in @obsidian monolith dm and uploaded the image here to not make it messy
we just want to make sure that there’s not people who we know/have reason to suspect are <= 12 that are on the server. if they claim to be 13 then we have no way of verifying this but this is at least in line with tos of not willingly allowing people who claim to be under that age on the server.
i used gpt to turn my idea into latex
yea ai doesn't know what preamble texit has so it sometimes uses some extra package and texit can't render it
I see
Thank you for your explanation, smay!
if you think i copied the identity mentioned here from gpt, well i was making it here by using Π(k=1→n) k, what do you think i was typing for 10 mins 
I see
Also @lyric meadow If I claim to under 13 eventhough I am 16, Will you mute or ban me?
she will if you ping her 3 more times claiming the same
You've got brain to derive identities
She*
mb
fix the other pronoun too
if you actually claim to be under 13 you will get banned yes.
did you learn Π from your classes or online?
Nopw
my own little brain
understood
good 👍 me too 😂





