#help-23
1 messages · Page 408 of 1
Ok so i think
That
A mixture of 50% oil and 50% is poured to fill up the entire container
After a few days
The bottom part will only be occpupied by the water
And the entire oil will be in the top part
The line through the middle is basically imaginary
What's the question actually?
Which of the pictures describes the process the best
Ohh
FINALLY
But im not sure if the oil graph only describes the oil from the top container
Can i also see the oil in the bottom container on that picture?
Ok so is this correct?
Yes
Okok
Lwts look at the starting image
Why are there 2 vertical lines
In the bottom left and top right
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why cant we say log 2 to the base infinity tends to 0?
you cant really have infinity as a base
you can say the limit as b approaches infinity of log_b (2) is zero
on a more serious note, stop using infinity as if it were like any other normal number. it is not.
infinity is a symbol, not a numbe
idk if the sign matters here, but really, it's just $\lim_{b \to +\infty} \log_b 2 = 0$
1 divided by 0 equals Infinity
you can't say log base infinity. It's like saying log base some symbol. That purely doesn't make sense, does it?
so we have to take limits.
yes i meant it tends to infinity mb
ty
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Uh i need help immediately , for the first paper for b4 2<x<3 how come when finding the probability i can use the formula f(b^- )-f(a) so like 3 val i think is 1 but the closest val before is 5/6 and f(a) 2 is 5/6? thats where the little points/dots are at so it ends up being 5/6-5/6 but for the second paper the second graph we have 0<x<5 we do f(b)-(a) 1-.75=.25 what defines if we use the val just before or not is it if like each point is a jump like the first paper at x= 1,2,3 it goes up but the second paper it continues on 5,6,7,8,9 idk if im explaining my confusion correctly but could anyone explain the difference of how i find each probabilities 🥹 sorry if i sound confusing
This is just some practice problems btw nothing graded but my exam on this stuff is soon and im just confused on this part
@half berry Has your question been resolved?
Help🥹
I have a difficult time decoding your doubt, but what's always done is, you compute the area of F'_x in the interval [a,b] when P(a=<X=<b)
Hmm uh let me try and reexplain so for the first paper for question b4 they have 2<x<3 and to find the probability they do the value before f(3) minus the value of f(2) but for the second paper when we have 0<x<5 they do the value of f(5)-f(0) what defines if we do the value before or the exact is that a better explanation of my confusion 🧍♀️
Ok I see
So because the first page all the numbers have like an end point and a starting to the next jump we calculate the probabilities differently?
So when we have 2<x<3 we take f(3) before the jump which is 5/6
But since 0<x<5 5 doesnt lie on some like jump its just on that line we take 1- the (0)
?
The point is, if the jump is not on the endpoints, then in continuous distributions you can "ignore" them
IF they lie on the endpoints like in 2<x<3 <- the 3 here, then you don't bother entering, you are just enough interested into what happens really really close to 3 rather
the thing is < 3 means you never reach 3
so you can actually get to the jump
Oh
That does make sense
That’s why its the value just before
Okay thank you
My exam is in like 10min😸
Good luck!
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hello
@nocturne lance Has your question been resolved?
<@&286206848099549185> PDE/ODE question. this should be within my abilities I'm just having a hard time for some reaosn
idk maybe like 4 or something
pardon?
sorry im not sure what you mean
no im just joking idk i cant really help on this sorry
mb for wasting ur time or anything
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Hey
please send your question if you have one.
Oh yeah
assuming it is, what have you tried and what do you not get?
Wait let me try it again
sure.
I keep getting like -4s to the power of -9/-5s to the 4 and it says it’s wrong
well first of all, you have a negative exponent, and second of all you have not simplified the fraction.
also, the -4 is wrong.
by the way, use ^ to denote powers.
Do I start it off by like multiplying -3 and 3
that part is not wrong. but don't forget that the -4 is there as well.
What now?
don't forget the -4 is in the brackets as well.
the cube of 4 is not 125, I'm afraid.
Oh it’s to the power of
did you just do 4 x 3 = 12
Or something
I mean I presume you took (-5)^3. which is wrong.
oh wait that's an s, my bad.
so no, -12 is even worse, that's (-4)*3, not (-4)^3.
So 64?
do you want to try it yourself first?
Yeah
sure, go ahead.
correct.
Am I done?
no.
Don’t I do the quotient rule or something like Subtract the exponents
yes.
no.
What did I do wrong
why is there still a t in the numerator?
So 3?
rewrite your fraction.
correct.
I don’t think I can start this one
why not?
It doesn’t look like the other ones
in what sense?
It’s bigger
doesn't matter. the same strategy works.
Alright so do I start with the parentheses first
well you should.
A negative times a positive is a negative right
yes.
Alright what now
do what you were doing earlier, letter by letter.
Do I subtract
subtract what from what?
The exponents
yes, if you mean applying the standard quotient rule of exponents.
Is this right
no, for several reasons.
Dang
your p and x are both unsimplified. why are two of each still present?
After I subtract the Exponents what happens
nothing? what are you expecting to happen other than there being only one instance left of each letter, anyway?
you should have exactly one p and one x left after simplifying.
Oh um I don’t know
show your work after your subtraction.
correct, though could be a little neater.
4^4. there's nothing indicating multiplication here.
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Did I do this correctly
we don't have enough information to determine what you were supposed to do
Oh sorry
I forgot to send the question
not this being the same q as the channel above 😭😭
Determine f’(-5) estimate to 1 decimal place
reasonable approximation i guess
Will it work?
yeah
Oh damn a clsssmate in here
just haven't seen that method of approximation before
Wait where did u get this
but ig it's a better approximation then the normal limit version
The message links to the channel 
😭😭im lost
Ok so should I continue it
is it -1/2
this finding average ROC over [5-h, 5+h] thing
i haven't seen it used as a method before
but it seems like a sound method
The teacher never taught us this 😭
(I'm guessing that you may be expected to draw a tangent line, and find the gradient of that?)
How will this work
If you'll excuse the shit diagram, draw something like the purple line, and then find the gradient of that, which does appear to be about -1/2
👍
Thank you
(that may not be the way they intend you to do it, but it is a way I have seen that questions like this are meant to be done
)
👍👍thank you
i feel like drawing tangents is weird
like u gotta be really accurate
didn't someone already answer you in your own channel?
It can be, I'm not a fan of doing it that way, though at least from the experience I have, there's some leniency given for the answer you get, though take that with a pinch of salt and all 
Sorry @junior smelt but I had the same question as ram
For question 26
Josh said where it’s steepest slope but not maximum value I think
Yeah, steepest slope, "where are you increasing the most" 
Ohhh
Wait
Doesn’t it say maximum value
maximum value of f'(x), not f(x)
the value of the first derivative at a point is exactly the slope of the function at that point.
(Maximum value of f'(x), the derivative
)
so the maximum value of the first derivative of a function is exactly where the function is steepest.
Yea I thought it would be highest at x =2
For f’(x)
Yep wouldn’t it be at the end of the steep
the derivative doesn't exist at x=2, though
you have a sharp point on the graph
no.
Ohh so cusp doesn’t count
yes
So x = 1?
be very careful: just because a graph is continuous, doesn't mean it's differentiable (at a point).
yes
(you could say something about the one sided derivatives there, but you gotta be careful with how you state it)
derivatives can fail to exist if
f is discontinuous at x=c
the slope of the tangent line from the left is not the same as the slop of the tangent line from the right of x=c (sharp point on graph)
or
the tangent line is vertical (infinite slope)
@cunning zinc
at least those are typical ways derivatives can fail to exist
well if it was obvious for the helpee, we would not be here. let's not treat a fact as obvious first.
fr
<@&268886789983436800>
<@&268886789983436800>
(to be fair, it seems like they're classmates 
)
that's fair. this cat shall refrain from further commenting on their behaviour for now.
26
I didn't say x=3
I said on [0,3] is where the function f(x) is increasing at the greatest rate
from x=0 to x=3
just by looking at the graph
@cunning zinc
Oh
Not the maximum value then
So would it be around x = 2
and actually, I misread it
it should be on [0,2] where f(x) is increasing at the greatest rate, not [0,3]
the derivative does not exist at x=2, though
Cusp
yes cusp/sharp point
- is simply asking the what the maximum value of the derivative is, not at what point that maximum occurs at
but yes, it would be infinitely close to x=2
but not at x=2
to answer your question @cunning zinc
Oh
Ok that makes thank you
No problem :D
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I need help understanding this with Trigonometry.
you only need to remember the top right quarter because everything else is symmetric
Alright, but what does it actually do?
what do you mean
Well, I see it. But I have no idea what we actually use it for.
it’s just like a fact
Well...🥀
it tells you the coordinates of a point on a circle some degrees around
and you know points on a circle are of the form (cos theta, sin theta)
Yes,
so its just a few examples of pairs of theta <-> cos,sin
this is some values of sin and cos
it lets you avoid using calculator sometimes
Hey kira can you help me with one?
About what??
why is bro trolling
IDK
Oh I see now lol where is the math stuff at lol
In another help room.
Which one
Any...
This one
No... you are actually going to get reported by someone.
Alright fine
<@&286206848099549185>
?
I am having trouble with this UNIT CIRCLE
!status
What step are you on?
1. I don't know where to begin.
2. I have begun but got stuck midway.
3. I got an answer but I was told that it's wrong.
4. I got an answer and would like my work checked.
5. I have a question about someone else's work/solution.
6. I have completed the problem and don't need help anymore. Thank you.
7. None of the above
No.?
1 to 2. I would say 1.5...🥀
I know what it is, I know how it works. But, I have never done anything with it yet.
Rounded up what is the closest 1 or 2 😭
1
Not really rounded up but closer to a one.
Letmetrytounderstandbrb
Close enough?
On the unit circle every point is written as cos θ, sin θ, which means the x-coordinate is the cosine of the angle and the y-coordinate is the sine of the angle.
Wait can I see the pic again?
Does this help
So... if we had cos(sqrt3/2) and sin(.6) how would we do that?
You said you knew what to do 🥹
I said I know what it looks like. I know what the lables are... not what to do. 😢
🥀🥀🥀
For cos(sqrt3/2) that's like asking what's the cosine of an angle that's sqrt3/2 radians? Back of the circle, I saw cos(30°) or cos(pi/6) = sqrt3/2, so answer is sqrt3/2. For sin(.6), need calculator, sin(.6) ≈ 0.56.
I just asked my friend that her name is iris thanks to her for telling me what to type 😛
I just put Everything that she said 1-1
Is she here currently?
Ok, so when mapping it then we would make the first mark from where the Hypatanuse and Opposite converge at 30°?
It's midnight I don't wanna think I'm on a call with her I'll just ask her 😭
It is also midnight for me... so...😓💀
So you're plotting 30° start at the positive x-axis, move up 30° counterclockwise and mark the spot. That's (sqrt3/2, 1/2).
Why does she sound so weird talking to me 😭
Yeah, that is what I thought. Ok. So, what about Sin(.6)?
I don't wanna think let me ask her 🥹
Yes. So, what do we do with .5646?
She said use a calculator to get the exact decimal
And then do what with the Unit Circle?
I feel like she's using ChatGPT...
Wait imma ask her to open her screen
SHES USING CHATGPT WHEN I WAS ASKING HER 😭😭
She has a 1.2 gpa 🥹
🫡🥀GG we are cooked.
I don't wanna think and she's using ai which is agaisnt the discord server...
ask someone else I wanna sleep 🥺
Find a mod or a helper
But. Who needs sleep these days?
ME I HAVENT SLEPT IN THREE DAYS.
It only is if someone knows about it. And, I didn't here anything
That makes four of us.
Four?
FOUR
Four?
FOUR
Four?
okay wait, so what remains as the question?
What do we do with .5646 as sin on a UNIT CIRCLE?
I understand what we do with Cos
But about Sin
🤔
Yet I asked me about cod 🥺?
did that value come from somewhere else, like a calculation or something?
Yes, sin(.6)
so you found out that sin(0.6 rad) = 0.5646. but in what context are you finding this value?
otherwise this appears to just be a random calculation.
Just simply sin(.6) cos(sqrt3/2)
I just assumed values for sin and cos to know what to do with them on the UNIT CIRCLE.
so you want to find the final value of sin(0.6 rad) cos(sqrt{3} / 2 rad)?
You assumed?😭
Well, I want to know what we do with those values on the UNIT CIRCLE.
or, what exactly is your original question?
Her status was 1
What do we do with sin and cos on a UNIT CIRCLE.
nothing? it's a reference to the sine and cosine of those angles.
Basically WTF do we actually do with a UNIT CIRCLE and how.
you use it to understand the signs and behaviour of the sine and cosine functions (and indirectly the other circular / trig functions as well).
Yes, how would I go about that?
by using this concept and relating it to the circle with values you gave.
So... how would this work. "t" is the arc, yes?
t is the angle between the positive x-axis and the given line.
this angle is always taken counterclockwise.
Yes, so ot is simple to see with a protractor and such devices.
well most of the time the angle will be given or information is given for you to find it, so.
So, then how do we define the line on the picture other than positive x?
unless the topic at hand is geometric constructions.
the same way you do for positive x.
just rotate the radius a tad bit further.
How do we know what is 'just a tad but further'?
if you wish to ask a question or ask for clarification, please use a message. a ❓is interpreted as something wrong with the statement.
Ok, I see
you said other than positive x, so negative x, I suppose. then just rotate the radius until it's pointing to the left instead of to the right.
the unit circle works for all possible angles from 0 to 2pi radians (or 0 to 360 degrees).
and the coordinates of the point on the circle where the radius intersects are always (cos t, sin t).
Well, I am not talking about x. I am talking of the line that also spreads from the middle that is darker than the rest
I don't see any line that is darker than the rest.
so the radius.
Yes
it's the same darkness as the rest of the circle, but I digress. also please don't spam reply pings.
ok, so what's wrong with the radius?
Like, do not press the respond button before sending a message responding to a statement you made?
I was just curious how we determine the radius and it's position.
no, but rather turn pings off.
I don't get what you mean by determining the radius and its position.
The radius is going to be the appotanuse of the triangle, yes?
the hypotenuse of the right triangle in consideration, yes.
So, how do we decide where the hypotanuse is. Like, how do we know it goes there and not in any other billion other ways?
by looking at the positions of the adjacent and opposite sides as well.
So that is what we use cosine and sine for here?
it depends on what you mean by use.
if you mean for the coordinates, yes.
if you mean for some other purpose, then I don't know what you mean.
Well, if cos(sqrtx/3) and sin(.6) then what?
Please show the original problem, exactly as it was stated to you, with the entire original context. A picture or screenshot is best. If the original problem is not in English, then post it anyway! The additional context might still be helpful. Do your best to provide a translation.
I will not entertain two random values without any context whatsoever.
I am trying to figure out how we form a triangle on the unit circle. I am new to trig and told this is what I should work on first. So, all I know is that cos(sqrtx/3) and sin(.6) are values that will form a triangle within the unit circle.
I am struggling with the actual formation of the triangle itself.
show the original question on paper or on the website or in whatever resource you are using.
I don't know how to form these triangles. I see them, but I do not know how to put them there or create them.
once you've drawn the radius on the circle, draw the line from the radial point (henceforth, this term will be used to refer to the intersection point of the radius and the circle) to the x-axis. that's your opposite side.
then from the origin, draw a horizontal line to meet that opposite side. that's your adjacent side.
that is if I interpreted your question correctly. if not, then I don't know what you're asking.
Ok, I see.
Thank you, this is what I have been asking. I suppose I got bonus information. Thanks.😊
please do not spam reply pinging.
you can reply ping from time to time, but don't reply ping on consecutive messages please.
too many pings in a short period of time is annoying.
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can anyone help me pls
For the part a), are you sure the range you stated for E is correct? 
(Also, ignoring that for a second, can you take square roots of negative numbers?)
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oh yes that is right
it alr in the equation of E(x)
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considering I have $f(x) = {e^{x+2}+3}$ so i get smth for ... x value. but i sometimes learned that the +3 is some sort of constant and so.... what does each number mean here
PainAndLight
f(x) is a function
It takes an input, here it's x, and returns an output
yeah i know, but like. but iirc there was like a reason there was the constant there
maybe i confuse something here
but I think I could without evaluating the whole fnc that the func will look like ... postive or neg
It could have been e^{x+2} + 49090
That is something that basic exponential functions make pretty clear, yeah
or constant cost
Please show the original problem, exactly as it was stated to you, with the entire original context. A picture or screenshot is best. If the original problem is not in English, then post it anyway! The additional context might still be helpful. Do your best to provide a translation.
no its example in my head
like saying the function evalutes the cost each month... +3 would be like i get 3 dollars each month from my granny
We take an x
Raise e to the power of x+2
So for example if we pick x = 2
We raise e to the power of 4
And then add 3 to that
e^4 + 3
Uh, no
Because that's your function
$f(x) = e^{x+2} + 3$
ok, ill look up e again, i forgot its meaning
It's the Euler's number
Well let's say it did tell us some random cost each month
At month 0
The cost is f(0)
yes
i mean
The + 3 actually increases the cost by 3
ok ok
If you had -3
yes
Then you could perhaps think about it like "grandma gives me 3$ each month"
ye
So the cost is 3$ less each month
thats good
You add 3 everytime, no matter what x is
yeah, now i can kinda assign the numbers to some realistic value
What do you mean?
is it true that there are formulas that have no real real life occurence yet... like theyre completly theoretical
i mean like money growth
Oh, yes
If my bank balance grew exponentially, I would be very happy
Sure
:O
I mean, many theories, formulas etc. were found without clear practical usefulness at the beginning
ill start a business that grows exponentially, in very tiny small steps
weird
But now they are used all the time in fields like electrical engineering, quantum physics, etc.
A lot of math is discovered a significant amount ahead of practical uses
thats weird.
but I think its costly more effiicient to raise a math genius than build smth and hope it works like imagined
Well, not really if you think about it
Mathematicians are interested in the patterns that many different things have in common, they rarely care about how one thing works in a specific case
And in the end, mathematicians are simply curious
mhhh
math is weird. (everyone) can learn it . "simplest" math has good appliance. and it seems to have literally universal meaning
anyway
thx
ill close now
Yes exactly
:)
yeah
yeah m2

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Hey there
Sorry, i am INCREDIBLY bad at math and always have been and I’m studying for an exam where I’m really confused
just give the question
The correct answer is B
How does drama club have 50% more participants than science club
Wouldn’t it need to be 40%
here's the thing
its not the percentage of the total
but the percentage of the particpants in the club itself
i think
also strangely they're both false statemets
i think this is a mistranslation
what's the original
okay
statement once says: that sports club has double the members of chess club
but 35 is not double of 15 which is 30
so do you understand?
yes makes sense
just #2
Ohhhh i think i understand
50% of the science club is 10%
now for the second statement, it says that the theater club has 50% more than the other club
so 20%+10% is that 30% then
yeah 50% of 20% is 10%
so do you get now?
its not the percentage of the whole 100%
but only the 20% of the science club
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hey guys I was working on 6
and I had to use the solution bank, basically I get everything about the method of the quesiton
Okay, part a?
EXCEPT the beginning
because it says it's 2 angle in a triangle, but the solution I followed represents it as 2 different triangles
and that's got me confused
this is the solution im doing
Ig they did that for simplicity
right but if you tried to put it on the same triangle
it wouldnt make sense right?
since one angle's opposite would be the other's adjacent
and they dont share
No it would make sense, it'd just be a bit complicated
could you show me cuz I cant imagine it
I tried to do it
so one angle I say the opposite is 3 and the adjacent is 4
when I go to the second angle it just falls apart
like no matter what I choose
I mean how I think of them
Imagine a non-right angle triangle
Wait can you draw and send pics of it, just draw a random triangle ABC
(Not right angled)
Okay, now draw a perpendicular from B to AC
Okay, now name the intersection D
So BD/AD could be different from BD/CD
But it's technically the same triangle, you're just focusing on parts of it
Eh TBF depends on how you want to say it, but yeah, I've shown you how to visualise it
hmmmmm
the only thing is like
how can you say BD and DB could be different
that's exploding my mind rn basically
Oh wait no no, I'm not saying that
It's like 5 and 5 are same
But 5/7 and 5/13 are not
right
I think it's because they don't share the same opposite (numerator)
that's really irking me
I mean if thinking of it as two different triangles helps you, then yeah go ahead
But it's not entirely two different triangles
Think of it more like ABD and CBD
ahh ok and they both share 12 as the adjacent
that way it could with BD as 12
since tanA is 9/12
do they even have to share it though?
You could say that, BD = 12, AD = 9, CD = 5, and AC = 14
Yes, because they've specified that they're two angles of the same triangle, i.e. ABC
yeah they'd have to share one line i guess
but man this feels so
what you call it, arbitrary?
IDK im still not really clocking it
Well when you're looking at a question, look at firstly finding the absolutes
Two angles A and B in triangle(ABC) are such that tanA = 3/4 and tanB = 5/12
So, they've said they're two angles in ABC, that means it's one triangle
Also, do you know about inverse Trigonometry?
like arctan stuff?
yeah
And arctan(5/12) is, eh, roughly 23 degrees
So it's basically just a way of showing angles, if it helps you think like that
Yeah thinking about it as just an obtuse triangle with those angles
that happen to have a tan ration of whatever
is a bit easier but
I think im fixated on opposite/adj
Yes, almost all angles are like that, any scalene triangle, and if you draw a perpendicular from one point to the opposite line, the ratio basically matches the inverse Trigonometry ratio you get from the angle you already know
but yeah the triangle is obtuse so thinking in terms of opposite/adj is probably the wrong way to go about it
Yup, I mean you still can, you just have to draw a perpendicular from one point to the opposite line and then work with that as two right-angled triangles
It's better to think of it like that with invisible perpendicular inersections ig
Yup, it's always easier to draw and then think about it until you're proficient
I think I get you but even in the above explanation tho
like here
Yes?
This lets them share BD as the adjacent 12
but now we're not even looking at tanA and tanB
We're looking at tan ABD ect
Which is really tan(180-(A+90)) ect
like it's just not really clicking into place
wait a minute thats just tanA
wtf
Oh wait yeah, that's just tan(A)
Ok I think imma leave it here and hope my brain computes this in its own time
cuz rn im not getting it haha
Yeah I mean just think of it in terms of inverse Trigonometry, that helps
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Alright then, also you could wait for a better helper
ahh it should be fine u did great
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In page 81, question 39 of Stewart's Calculus the problem states:
$
f(x) = \begin{cases}
0 \text{ } \text{if $x$ is rational} \newline
1 \text{ if $x$ is irrational}
\end{cases}
$
Prove that $\lim_{x\to 0}f(x)$ does not exist if $\lim_{x\to 0}f(x) = L$.
Toaster
\\ not \newline gng
In page 81, question 39 of Stewart's Calculus the problem states:
$
f(x) = \begin{cases}
0 \text{ } \text{if $x$ is rational} \
1 \text{ if $x$ is irrational}
\end{cases}
$
Prove that $\lim{x\to 0}f(x)$ does not exist if $\lim{x\to 0}f(x) = L$.
Toaster
use sequential definition of limit
What have you tried
Honestly I've been just staring at a blank page for 60+ minutes and everything I've done just ended up nowhere
This is so me
What is the sequential definition of a limit?

Interesting, the book's never told me yet
a sequence ${a_n}$ converges to a value $a$ if, for every $\epsilon > 0$, there exists some positive integer $N \in \bZ^+$ for which $|a_n - a| < \epsilon$ for every $n \ge N$
basically, if a sequence gets arbitrarily close to a value eventually, the sequence converges to that value
So it works for my piecewise function?
A function $f: \bR \to \bR$ has $\lim_{x \to 0} f(x) = L$ iff, for every sequence ${x_n} \to 0$ (with $x_n \ne 0$), we have $f(x_n) \to L$
so what you should do is find two sequences that converge to zero, but when applying $f$ pointwise to those sequences, they converge to diff values
i.e., find two sequences ${x_n} \to 0$ that give two different limits for $f(x_n)$
@calm stream is this covered in your book?
i just realized this might not be an analysis question
I'm in the epsilon-delta section in the first cchapter of stewart's (idk why it's here), for refrece i had to google what $f: \bR \to \bR$ is
Toaster
f: R -> R just means an ordinary real-valued function
did he discuss sequences and how they converge at all?
if not then you should do this with epsilon-delta
then what definition of limit did you learn
Yeah, I was thinking of doing it with epsilon-delta because sequences are in chapter 11 of the book
are you familiar with this definition?
For every $\epsilon > 0$, if there exists $\delta > 0$ such that if $0 < |x - c| < \delta$, then $|f(x) - L| < \epsilon$, then $\lim_{x \to c} f(x) = L$.
Yeah, that's the formal $\epsilon, \delta$ definition right? Where the $|x-c|$ part is the distance in the x axis from c and the $|f(x)-L|$ is the distance in the y-axis from L right?
Toaster
yes
wait this is stewart?
Yeah
well i'm not sure how formal your proof is meant to be then
are you familiar with the density of the rationals/irrationals in the reals?
wait, what's that?
if you have any interval in the reals, you can always find a rational/irrational number in it
for example, if $a, b \in \bR$, then the open interval $(a, b)$ must contain infinitely many rational and irrational numbers
Oh yeah
did your book/class/wtvr teach you that?
No, I'm self-studying through the book
did your book teach you this property of the reals though
from my understanding stewart isnt really a rigorous calc book
It's in the appendix
then you can force a contradiction here
assume $\textstyle \lim_{x \to 0} f(x) = L$. then, for every $\epsilon > 0$, there exists a $\delta > 0$ such that $0 < |x| < \delta$ implies $|f(x) - L| < \epsilon$
so $x \in (-\delta, \delta) \setminus {0}$ (x can take on any value in the open interval $(-\delta, \delta)$ except $0$)
note that any open interval in the reals must have a rational and irrational number, then choose a value of epsilon to contradict this statement
i hope this makes sense
Oh yeah, so all I have to do is to find a value of epsilon so that $|f(x)-L|$ isn't less than $\epsilon$?
Toaster
what is the value of f(x) when x is rational? when x is irrational?
since you know $x \in (-\delta, \delta)$, $x \ne 0$, you know $x$ can be either rational or irrational. what does this mean for $|f(x) - L| < \epsilon$?
for rationals $|-L|<\epsilon$ and for irrationals $|1-L|<\epsilon$
Toaster
Yes that's very good
Now show there's a value of epsilon where both of these statements cannot be true simultaneously
That is, find a specific value of epsilon
Ohhh, $\epsilon \leq 1/2$?
Toaster
,w solve |x| < 0.5, |1 - x| < 0.5
Yep
So you have a contradiction
So lim x->0 f(x) is not L
Meaning no limit exists at 0
Hope that helped :)
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Hi there im confused about how I labelled these forces
I dont know where to put Fr
what do you mean "where"
in eqautions or in diagram
as in diagram you have put it correclty
Friction always acts parallel to thr contact surface
Oh Fr is friction, not reaction force?
Also what is H
Oh well then
So wheres that sorry
Thats what i was wodnering too
Those are not forces
Well just think using your real life scenarios
where do you think it would be
No i know that but in the mark scheme it says this
do you mean the normal forces?
Meaning that H has to be vertical so on the wall
Yes, my teacher just says use V and H
for those type of questions
That horizontal equation is correct but you have made it wrong
Horizontal means parallel to the earth right?
horizontal means perpondicaler to g pooling of earth
Yeah and why have you mde it verticsl in diagram
they just took a differnt angle
Because once i resolve up and down it says Tsintheta = H
Ohh
so my angles are wrong?
-# hes not at taht level yet gng
For T
no they are correct
she and yeah im not 😭
You can take different angles
for example you took angle of string with horizontal, your teach took one with vertical and string
sorry abt that misgender
Okayyy so i just need to keep it consistent and i'll get the same answer?
Its ok
Well Fr is always perpendicular to the surface of contact force
dw
Yeah but Fr isnt right direction
so its meant to be like this?
aka H in this case
so from my understunding the think is not moving so what suppose to happen is if you combine both the force of the string and the wall you should get a perfect vertical opposite to g
Thats right and thats what we are doing no?
to g?
Hold on i think you rteacher took V as friction force
whats p
I dont think so
isnt p the particle
wait so is this right then?
if Fr is perpendicular to V
no
Fr should be in the direction of V
😭
Same way??
No no hold on a sec
Sorry im so lost
i study physics in a different language so sorry if i miss up the symbols continue with the guy it is better than get confused with me
Yeah its ok thank you for trying to help though 😺
Just maths here
Plus im in england so maybe thats why its different
Right lets go back to direction of wall forces
💀 yea fr
-# oh am indian😭
Ohhh niceee different ethnicities
Right so well as your teach rightly said, there are two forces of wall acting
One vertical and one horizontal
Yeah
Well what the teacher forgot to mention was that the vertcal force is taken as friction here
Oh wow
Technically friction is a wall force right?
Well it does push the wall does it?
You can slide your hand down on a vertical wall
like irl rn
and tell me does friction slow down your hand
or does it push you rhand away from the wal
YEAH!!
Ohh ur so smart
So well now thats your fricton settled
Had to really think about that one 😭
😭
Np but, qsn isnt done tho
Yeah well where is friction or as your teach calls it "V"
Correct the diagram
this is the whole question btw
Its down
yeah i got that its asking tension
well not exaclty, its actually up
Oh yeah sorry so when my hand was on the wall, friction acts in the same direction
wait if you slide your hand down, its going to be up, if you slide it up, its going to be down
so well
Yeah!!
as a general rule friction is always opposite to the direction of movement
Its in defn of friction that its always going to oppose relative motion between any two
Ok thank you :)
let me try redraw it
Sure
so Fr is V as well?
Yeah!!
Yayyyy
You're so helpful thank you so much yajant 🥰
While im at it can i find another quick question just to see how to find angles
legit better than my teacher
You wlcm!!
and thank you as well no
nox
Sure
-# thats kind of you to say but please do be respectful to ur teach😭😭
you're right mb 😭
all good then!!
Hm one sec lemme read
okk and let me give the full question if u need it
Yeah thast better generally
yeah true
like with these questions the hardest thing for me is labelling the diagram
ill try and could you please see if im correct
holdon
you are welcome, another problem you are a hard-working good for you!
thank you 😃
you too
so essentially, i dont know if the forces are right
and for P
Idk where to put theta
angle
right heres a trick, for friction, even if you assume direction is wrong, you would just get negative value when you caclualte
Ooooo
So smart, love that
Okay so if its negative it just means it'll be in the opposite direction
So even with this question did it even matter lol
But u just had to know if it was up as opposed to right
Yeah but its better to do it correctly right😅
I think he get's it right thought
and also, your Qsn are elementary so far, which is why this will work mostly
true 🤣 but its good to know
elementary?
it should be at the right not left
for this question?
he meant not university level i guess
oh okay fair enough yeah
I did something similir in highschool physics (never in math)
yea i did in maths too
basically last year of high school
yeah bane of my existence
anyways how will i label theta
for P
is there a trick for that?
i always get confused
yeah but not uni also, even higher physicis in school (what i am doing currently) too
wow smart lad
mechs in maths will usually be different
yeah true
9.8 is used for gravity in the spec i did
Well so have adam and NoX got it covered orr?
😭 such a small difference but makes sense
yeah pendulums
