#help-10
1 messages · Page 531 of 1
Yeah
I thought generally when someone says f is invertible, they mean it’s both left-invertible and right-invertible
Just like “associative”
Should probably look those terms up
We learnt about inverses in discrete math before calc
in dm it had to be a bijection, but in calc, only an injection was enough
Right right
And we never ever dealt with invertibility
Or injections or surjections or any of that
But it makes sense that calc only cares about left-inverses
Wait I’m like
Forgetting what a left inverse means
Why is that sufficient? I don’t know why I just said that it makes sense
g(f(x)) = x, right? Not necessarily f(g(x))?
Hmm...
Oh but
You can restrict the range R to the codomain and its surjective then
Right?
Instead of having f: R->R, do f:R->R* where R* subset R
and for every f(x) in R* you have an x in R that maps to y=f(x)
=> f is surjective?
Yeah
Ohhh
I feel like this relates to partial functions
Which is also a calc-only thing
What are partial functions?
It’s like a function, but not every element of the domain has to map to something
It’s like how f(x) = 1/x is considered to be R -> R
Well not literally
But like
A partial function is often used when its exact domain of definition is not known or difficult to specify. This is the case in calculus, where, for example, the quotient of two functions is a partial function whose domain of definition cannot contain the zeros of the denominator. For this reason, in calculus, and more generally in mathematical analysis, a partial function is generally called simply a function.
Aha
"a partial function is generally called simply a function"
Lets define a whole term that we wont even use
lmao
That confused me for a while
So
If you think of functions instead as partial functions
Then for a “function” to have an inverse, it only needs left-invertibility
That didn’t really make sense lol
Whatever
What's even the question ;-;
Would you believe me if I told you there isn't one x)
Yes I would belive u
Reopen it
I think the bot glitched
Yeah
I guess surjectivity will fix the swap between domain and range?
Hmm
What even is an inverse
Lemme draw this
I have absolutely 0 intuition right now
if f:A->B and f^-1: B->A
f: [0,2]->[0,5] w range [0,3]
f^-1 : [0,5]->[0,2]
but f^-1(4)=??? because it's not a surjection
There's a two way street between each element from A to B, would be the proper description I guess? ops, no
oh god ive confused range and codomain
Can I see?
Oh... g isn't a function
But if functions are really partial functions, then f and g are perfectly good inverses!
No, I don't think it is ok to do these definitions under partial functions
Also, didnt it say partial functions are functions? Not the other way around o.O
Ok here's my question: f is injective. That means there exists a function g such that g(f(x)) = x for all x in X. I've drawn g here, so what does 2 map to?
No it said in calc partial functions are often simply called "functions"
Nothing, because it's not a surjection

But then it's not an injection
Oh right
Well yeah that's the way to go
I think I'm having some discrete math class flashbacks
Here's a question though...
f can't possibly satisfy f(g(x)) = x
If f is an inverse of g, isnt g also an inverse of f?
left is injection right is bijection?
ye ye i just googled it
See the diagram, g is surjective so it can only have a right inverse, f (which is shown to the left of g)
God the diagram is very frustrating sometimes
Considering only the first 3 circles
f is on the left of g, but f is a right inverse of g
Man...
Wdym
So they're surjective by default
Yes
But in every calculus text I've seen, it talks about arbitrary functions f : D -> R, and they're including f(x) = x^2 in this theorem/Lemma/whatever
Ok I think
For sine, people understand that it doesn't have an inverse on R, so they don't call it "sin inverse" they call it "arcsin" (emphasizing that it is a different function). But everyone generally understands that injective functions like e^x have an inverse and so there's no name change
Ahh!!
What is it
I agree it's just that im having trouble typing sth
oh lol
What are you saying with this though?
I thought we were talking about functions not needing to be surjections to have an inverse
That is, the left right w.e one
Oh right
So then f: [0, +inf) - > R, f(x) =x^2 doesn't have a two sided inverse
I see what you meant with that now
Although what I meant was that we take it as a two sided because we make it surjective by restricting the codomain to the range
Those are my final thoughts
Ah yeah
abs_0
God I hate typing on mobile
Right
But thats because the domain is R^+-{0}
so x cant be negative on the right side
if it were
e^ln(|x|) then itd be |x|
with domain R
which is also why
f(x)=e^ln(x)
is not the same function as
g(x)=x
Yes?
Oh I suppose it makes sense
e^ln|x| = |x|
Cause (red then green) : R+ -> R+ is really the identity on R+
So it doesn't matter what the blue function is, as long as its range is R+
Well...
So then we could say for any function b: D -> R+, we have e^ln(b(x)) = b(x) for all x in D
Yep
It's good cause I can barely read so I like looking at pictures
Literally
Although your pictures are confusing a lil
Okay so in short: Calculus doesn't care about right-invertibility because you can make any injective function surjective by restricting the codomain to the range at any time, and the function itself wouldn't practically change. However, if you've got a surjective function and restrict the domain so that it's injective, it's not really the same function anymore, because then you can't input as many numbers as before. Thus inverses must have a left inverse, but don't have to have a right inverse.
Take care now, I'm gonna debate whether I should sleep or just go 30h without
Bye
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how do i prove that |a|=0 iff a = 0?
i know that it's really obvious but i don't feel good without a proof
and i know there's a property of the absolute value that says
|a|=0 <=> a = 0 (Positive-definiteness)
but how can i prove that?
you can individually prove the forward and backward implications of $\abs{a}=0\iff a=0$
dino
sorry but i don't really get that
hmm, does it make sense if I say if we prove $\abs{a}=0\implies a=0$ and prove $a=0\implies \abs{a}=0$ then that proves your iff
dino
yeah that'll make sense, but i don't know how to prove |a|=0 => a = 0 and the other way around
would appreciate if you can prove that
well let's try a = 0 => |a| = 0 first
alright
so we have a = 0, then it's clear that the absolute value of a is...?
by the absolute value definition if a>=0, then |a| = a. so if a = 0, then |a| = 0
if a>=0, then |a|=0 or |a|=a?
so if a>=b, then (what i think) a > b or a = b
if this is true, then what you said is also true i believe
yeah that's true but I'm just letting you double check your first sentence before
by the absolute value definition if a>=0, then |a| = 0
oh my bad
i did a typo
i meant if a>=0, then |a| = a
cool cool, this is good then
now |a|=0 => a=0
that doesn't quite work, you seemed to have used the to-be-proved statement in your proof
wait did I?
ohh right
unless you meant the 0 in |a| = 0? but that doesn't tell us much since in |b| = 2, 2 is greater than 0 but b could be -2
you could consider that |a|=b => a=b or a=-b (edit, we only need to consider the forward imp)
so |a| = b implies that a = b or a = -b?
yup, does that make sense?
aren't we kinda losing information? like the a>=0, then |a| = a or if a<0, then |a| = -a?
or is that not needed
the information of a>=0 or a<0 is only available if we know a, which we don't in this case, right?
i see
yeap we don't
so could you apply this to |a| = 0?
|a| = b if and only if a = 0 or a = -0 = 0
is that true?
|a| = b? I think you meant |a| = 0
my bad
|a| = 0 if and only if a = 0 or a = -0 = 0
perfect
so |a| = 0 if and only if a = 0 or a = -0 = 0 and by the absolute value definition if a>=0, then |a| = a. so if a = 0, then |a| = 0
thus, |a| = 0 iff a = 0

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what are all the values of x for which x^5-3x^3+2x^2>3
@glass palm Has your question been resolved?
I assume you could find the roots and do derivative tests?
maybe finding the roots is going to be hard
i still didnt take derivatives
i can get the answer choices if that makes it better
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I don't know what to do next
I can help out
is this after or before you differentiated?
The x^2 + y^2 is before I diff
ok then, try again from the begining
remember, once you have started differentiating both sides, you differentiate both sides at once
also remember that y is a function of x
meaning the derivative of y wrt x is not simply 1
Okay lemme try again
I got this but what should I do after that? Should I transpose?
again, the derivative of y with respect to x is not 1
the derivative of y wrt x is dy/dx
if you are still having trouble, i'll do half of this for you as an example. In this problem, the derivative of x+y is not 1+1, but it's 1+dy/dx. Or for example, the derivative of y^2 is 2y*dy/dx
Oh okay you multiplied y' to the y variable as d(u)
yes, aka the chain rule
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What are some examples of theorems that were derived from the idea that there are infinitely many real numbers?
what exactly do you mean
do you mean there being infinite real numbers in any line segment on the real number line
or that the real numbers go on forever
this
well
limits to infinity wouldn't be as useful
because you could only do them on sequences
Why could you only perform them on sequences?
but the real numbers not going on forever implies the natural numbers don't go on forever
so actually you couldn't
so you literally couldn't do limits to infinity
this would mean you couldn't have taylor series
which are incredibly important
@gentle turret Has your question been resolved?
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What do you know about the function?
Please do my question I can't find direction ratios of first line
mate you’ve been spamming this in already-occupied channels for a while now
just find a free one
do you recognize the function?
How is log defined in the first place?
Cz this Indian channel
Exuse me?
@lunar mortar I want you to check #❓how-to-get-help
Nothing wrong with reading the rules as for how server works right?
Not interested
We're not really interested either
Then no one is gonna help you.
Closed due to the original message being deleted
Can't u just help me rather than just arguing it's my exam on Monday
It's not my problem. Besides, you don't know how this server works. I can't help you in a wrong Channel.
No one is under any obligation to provide help
the least you can do is at least follow the rules here
If you want someone obligated to help you, you could pay a tutor
U guys r not kind I think it's okay
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when u rewrite numbers as polar form can’t we get infinite answers for everything
Remavas
Remavas
a bit too complicated for me i think
It's just the good old power series for e^x
wikipedia makes everything complicated
and you plug ix in
what’s the e^x power series??
You didn't have calculus yet?
we do other stuff in school
Well, it can be shown that $e^x = \sum_{n=0}^\infty \frac{x^n}{n!}$
Remavas
how
OKAY i’ll look it up
Unless you know calculus, you won't understand where it comes from
but you are free to try
yes
for example
1 = e^(2n i pi)
yea
for n any integer
yea
you're correct
And once you know taylor series
You can come back and understand where Euler's formula comes from
You can use Euler's identity
I think that would be easier then trying to use the Maclaurin series for exp(x)
$e^{i\pi} + 1 = 0$
Remavas
I mean, i would just sneak around and then just use Euler's identity
what do u mean with calculus
I mean calculus
oh
u mean (2e^(ipi))²?
But I mean that won't give him any insight into why it works. Might as well just use Euler's formula instead then
$e^{2i\pi} = \cos2\pi + i\sin2\pi = 1 + 0i = 1$
Remavas
I have no idea when the taylor expansion is taught under the calc 1 calc 2 calc 3 classification
Since I never took it in that format
oh okay
calc 2 it seems
ooo
But, if you're like me and try to find shortcuts and shit, just know that e^iπ = -1
cool
Use this to your advantage because like
It'll become extremely useful
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Hello can someone proofread this:
Let $\omega,v$ be even differential-forms. Calculate exterior derivative of $dw\wedge v - w\wedge dv$
@drowsy cosmos Has your question been resolved?
<@&286206848099549185>
<@&286206848099549185>
@drowsy cosmos Has your question been resolved?
@drowsy cosmos Has your question been resolved?
Trying to understand the rules of functions and when jt is continuous and not continuous
If anyone can direct me
Anyone?
<@&286206848099549185>
read #❓how-to-get-help
Definition of function continuity/discontinuity (page 3):
https://faculty.math.illinois.edu/~aydin/math220/lecturenotes/m220_Sec1_4.pdf
No d(wΛv)=dwΛv+(-1)^|w| wΛdv
yeah and |w| is even
So you are correct when w is a n-differential form where n is even
Otherwise it’s zero
Okay then you are correct
alright can i show you another one?
Sure
Enoo58
It’s true when w and v are even
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Basic question but:
If there are 3 items and 20 people that could win it, how would i calculate the winning chance the person has to win one of the items, doesnt matter which
woudnt that be the case if there was only 1 item to be won?
its still 3/20
15%?
@tropic frigate Has your question been resolved?
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am I wrong? 🤨
ye 1/4 is the correct answer
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i dont really get how i am meant to differenciate e^x
do i differenciate 4x first?
and then i differenciate e^x
sorta
so for me it would be 8e^4x and for d2y/dx2 32e^4x
so your answer is B
lemme show you a little tool
but for some like if e appears in a product rule, do i differenciate e first?
Solve derivatives using this free online calculator. Step-by-step solution and graphs included!
oh lol
Solve definite and indefinite integrals (antiderivatives) using this free online calculator. Step-by-step solution and graphs included!
and for antiderivatives
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how do i solve this?
@wintry stream Has your question been resolved?
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Hi, so if 2²=(-2)²
Than √2²=√-2²
The root cancel the square so
2=-2? Is there's something I'm missing here
.nai
Yes i know the answer is always positive, so this means that i have mistake with the brackets (order of operations)
Like i should have solve (-2)² first which is 4 or something else
Yes
Oh thx
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Hey guys I’m doing this assignment where u have to leap and calculate a launch angle. Is it the angle ur about to leap of the ground or when ur first in the air?
the launch angle is always measured from the horizontal
regardless of how high you launch it from
So it’s from the ground?
from the horizontal..
oh you mean the angle they launch from
they launch (within approximation) straight up
Like cos I have to leap right, I recorded myself in slow motion but idk which angle is the initial launch angle
so I’m not sure
@spiral maple
Yeah I'd think the launch angle is 90, cause it's straight up.
the launch angle should be less than 90 under any circumstances right?
@spiral maple
@winter heron Has your question been resolved?
most likely
but draw a curve and tangent to your curve at 0
easiest thing you can do is find the length you traveled and your max height
and model your jump
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can someone help me get the function
from the graph
i got (x+6)(x-3)(x+3) but its not right
Try putting in x=0, y=-9 in the function you get from multiplying (x+6)(x-3)(x+3)
if x=0, then using my function you get -54
which I need to divide by 6
so do i just put ((x+6)(x-3)(x+3))/6
I think so :)
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guys
the first way is wrong
but i dont understand why I have to first do factorisation
in order to solve limits
0/0 isn't 0
hmm
so first way is also correct but its impossible to do it that way ?
because error 404
The first method just didn't get 0, but then pretended it did
So I wouldn't say that's "correct", no
If you get 0/0, that's a hint that the limit may exist, but you'll need a better method
hmm
Often, cancelling something is the way to go
Ok
when x--> infinity
I just divide everything by the biggest x
is there explanation for that
Sometimes, haha. Depends on the limit in question
like i had this let me find
For example, limits with sqrts often don't use this trick
So multiplying by x^5/x^5 is like multiplying by 1. You're always allowed to do that.
Then, you have the lower x^5 cancel out the numerator
but why is it allowed when x-->infinity
and when x-->1 i need the different method
because if i gotten a task with x-->1 i woulda failed
i just thought its dividing by biggest x
You did skip a step. You do have this missing:
$\frac{2 - \frac{4}{x^2} + \frac{3}{x^4} - \frac{3}{x^5}}{1 - \frac{11}{x^4}}$
Kaynex
So when you divide top and bottom by x^5, this is what happens
When you allow x to get very large, every term that's divided by an x goes away, leaving 2/1
howcome 11/x^4
and others
oh ye
its like
dividing numbers exponents go in subtraction right
Because $\frac{-11x}{x^5} = -\frac{11}{x^4}$
Kaynex
ok ye
Now, this "disappearing act" only works because x is getting very large
If x is just approaching 1, this method doesn't work anymore
$\frac{2 - \frac{4}{x^2} + \frac{3}{x^4} - \frac{3}{x^5}}{1 - \frac{11}{x^4}}$
Kaynex
So you agree, you have this after dividing top and bottom by x^5
yes
If x is really big, then something like 4/x^2 becomes really small
oh yes
ok like
basically what im trying to do with this
is determine the limit on y axis
,w graph \frac{2 - \frac{4}{x^2} + \frac{3}{x^4} - \frac{3}{x^5}}{1 - \frac{11}{x^4}} between 0 and 10
So you can see on the graph how it trails off to the right
yeah
@inland thicket Has your question been resolved?
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I need help with finding the domain and range for the first question. I found the inverse though.
Talking about part a?
The inverse function:
Yes
It’s all the x-values that a function can have?
and range ofc
Exactly
So can you think of a number that can't be cubed?
0?
Ye
Yes
So then if the function is cubing
And you can cube all numbers
We know the domain is ...
-infinity to +infinity
Yes, but you would write it as $$x \epsilon \mathbb{R}$$
Alfie
Oh so how about in interval notation
i think in a lot of highschools they don't require that notation
so interval notation is fine
I can only talk about what we do in the UK 🤷♂️
yeah makes sense lol
If they accept -infinity < x < infinity
Ok
And then the range, can you think of a number you can't take the cube root of?
So would that be right in interval notation?
Mmm..
0?
So you're saying that no number, when multiplied by itself 3 times, equals 0?
No I’m saying the number 0
So the cube root of 0 is 0?
Ye
So it is valid?
Yes?
Yes. The cube root of 0 is 0
Ok
Yep
Therefore..
Yep
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map g is such g(x, y, z, w) = (2x - y, 3z + w, x + z - 2w)
what i did was to represent the map as x(2, 0, 1) + y(-1, 0, 0) + z(0,3,1) +w(0, 1, -2)
and found whether they are linearly independent or not
nvm
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- The weekly allowance of all the Senior High School students in the schools in a certain city has an average of Php 350 with a standard deviation of Php 20. A random sample of 60 students was asked of their weekly allowance.
A. Determine the mean of the sampling distribution of the mean weekly allowance of Senior High School students in this city. State the rule/concept that you have applied (1 point)
B. Determine the standard error of the sampling distribution of the mean weekly allowance of Senior High School students in this city. Assume an infinite population. (1 point)
@wild forge Has your question been resolved?
What is a php
@wild forge Has your question been resolved?
Currency
@wild forge Has your question been resolved?
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In what case is this triangle equilateral?
which triangle? triangle DCG? what are the cases you have in mind?
Yes DCG
GD=DC and angle ABC=120
Is it enough?
are the lines AG and BC parallel
No
then i don't think you can show that the triangle is equilateral
I have these options
yeah seems like all the options don't give that DCG equilateral
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well hello, i'm kinda stuck on my math homework about solving a murder mystery. the lore is basically:
you have arrived at the murder scene at 4:35 am. theres the lead detective there and he says he's been there since 3:45 am looking for clues. you're trying to figure out the time of death. you take the temperature of the body and its 84.5 degrees. more detectives come, blah blah, you see that the room's temperature is 73 degrees. you take the temperature of the body for the second time and find that its 74.9 degrees, noting that the time is 6:00 am.
we have an equation given to us to help with the problem, which is:
https://cdn.discordapp.com/attachments/957541993431584838/957542858871697428/unknown.png
what i know/have done so far is
rooms 73 degrees, which is Ta
the first time you take the temperature is 84.5 degrees, which i think is T0
the second time you take the temperature is 74.9 degrees, which i think is Tf
and the time is 85 minutes
74.9 = 73 + (84.5 - 73) e^k85 is what i get when i plug everything in (im really sleepy rn so something i plugged in might be in the wrong place) which if you add and subtract everything, and leave k on one side becomes -9.6 = e^k85
use log
which is where everything goes wrong, i cant take the natural log of a negative number
and leave k85 by itself
i can't, taking the log of a negative number is impossible
why did you get -9.6
74.9 = 73 + (84.5 - 73) e^k85
when i tried it, i get 74.9=84.5 x e^85
yes
ok
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How do u prove that sqrt(2), sqrt(3) and sqrt(5) can never be terms in an arithmetic series
?
question24
so where I should?
Read #❓how-to-get-help and you would know
but I do bad in English
Literally the first sentence in #❓how-to-get-help
Why are we doing n-1, o-1, p-1
nvm its arithmetic series
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hello
$\lim _{x\to 0}\left(\frac{tan^33x}{x^2}\right)$
robic
how i find the limit?
i get a 0/0 so i used a different approach
when direct substitution
consider finding a way to apply the limit identity for
lim as x→0 sin(x)/x
i did actually
,rotate
it leaves me with 9, but in the desmos website shows no graph
i tried to make ^3 to ^2 for both the deno and numer
but you can't just multiply by cos(3x)/sin(3x) like that
as that isn't 1
make it ^4
don't overthink it
and apply basic exponent laws
just like how you expressed sin^2(3x) as sin(3x) * sin(3x)
sin^3(3x) = sin(3x) * sin(3x) * sin(3x)
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I need help
recall basic algebra
kk
???
=v
the hell happened in the 2nd line?
@loud egret Has your question been resolved?
$z-zit=1+it$
I grind too much
Mosh
this is a linear equation in t...
this shouldn't be uni material
this is like.. grade 9
it's solving a linear equation
regardless, it's still well before post-secondary
.close
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Hello, how do I go about simplifying this? I know I have to use the Fundamental Theorem of Calculus [F(t = inf) - F(t = 0)] but I can't seem to get the value of F(inf) because it results in an indeterminate of inf * 0. I know F(0) will simply be 0 when evaluated.
This is what I tried so far, doesn't seem to get me anywhere?
is s>0?
exponential grows faster than polynomials
So, the limit would be 0?
si
Oh okay, I thought of that too earlier when I checked online graphing calculators. But I wasn't sure if just mentioning that is enough
you can prove limit of t^(a*n)/(e^(b * t)) is 0 for any b>0
Hmm how do I do that though? I tried manipulating the fraction to be a different indeterminate form earlier, but that got me nowhere.
oh alright, guess I'll try induction first
could also apply L'H n times to make numerator a constant
and denom still having e^t
The problem didnt really state a specific n though, just that its from the set of n=1,2,3,...
its still a fixed unkown constant
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6a help pls
that doesnt seem like a math question
doesn't matter
It is
h=(v^2)/2g use this
it's from a book titled
"A level mathematics"
ohk
plus kinematics is mostly mathematics anyways
true
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Is this right?
yes
Yes but -2^2 = -4 though
-2^2 is indeed -4
-2x-2=4
-2^2 is not the same as (-2)^2
So why is my scientific calculator when I square negative 2 coming up as negative 4?
because you're not entering stuff in the calculator properly
think gc interprets it as -(2)^2
yeh, you're not telling it to calculate what you want
it is saying 2 square times -
respectable calculators follow the order of operations
Sorry for wasting your time again 😂
It's again very amusing to me how many people get stuck at this.
Thanks for being patient again with me…….
I have an exam in may I will be using this channel a lot 😂
Right.
i can imagine how many times i got questions wrong because i typed it wrong in the calculator
*cant
.close
So can someone please remind me why putting the brackets around the number changes the answer
so like this
-2^2 is same as this
-(2^2)
which equals to
-(4)
how ever if you put brackets
(-2^2)
it is showing that you are squaring the whole -2
not just 2
Right so why don’t they just put the ^2 on the inside of the bracket in the first place?
i mean it means the same thing i think
wdym that changed everything.
im confused now
Right that is 4.
yeah
lol
Me again
In this one I understand why we have negative 8 but why has the plus symbol gone?
Actually I’ve figured it out
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Two functions are given by the regulations f (x) = 2x^3−150x and g (x) = x^2 + kx + 25−500, where k is a constant. The function f has a local maximum at the same point as g has a local minimum. Based on this information, determine the value of k.
@robust sleet sorry let's go here
@lusty vigil Has your question been resolved?
<@&286206848099549185>
Yeah.. why wouldn't the 25-100 be simplified in the question?
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Given the slope and a point, find the equation of the line in m = 3 ( -7,2 )
how do i find the y=mx + b given the slope and point?
slope-point formula