#precalculus
1 messages · Page 293 of 1
$\sin(2\theta) = 2\sin(\theta)\cos(\theta)$
Ann
also consider $(\cos(\theta) + \sin(\theta))^2$
Ann
@viscid thistle
are 2 vectors considered parllel if they are like on top of each other
for example <2, -1> and <4, -2>
I would argue yes
parallel if they're scalar multiples
Hi!! I was wondering if I could have help with my Pre Calc parametric a review!! I’ll send a photo, but i’m really confused and was hoping for some help on these 3 problems:)
How do I represent 2 equations into a parametric equation
like -4x-6y+3z-6=0
and 3x+2y+4z+2=0
nevermind I got it
can some one break this down please
its notation for function compositions
eg.
(fog)(x) = f(g(x))
which you should know how to do with a basic understanding of function notation
Aren't the vectors called "anti parallel" if the scalar is negative?
wut
I've never heard that term before
I guess you could use it but no one does
if vectors are scalar multiples of each other, people will say parallel regardless of what that scalar is
You can switch that equation to an imaginary form, which would be easier to figure out I think.
That's my approach to find theta following trigonometry properties
\theta = $(\pi n+tan^{-1} (\frac{1}{5}(3-\sqrt(14)))$ ; $n \me \mathbb{Z}$
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$\theta = \pi n + \tan^{-1}\left(\frac{1}{5}(3 - \sqrt{14})\right), n \in \mathbb{Z}$
Ann
Could I get some help?
with what?
Just do $\sine{x}+\cosine{x}=\sqrt{2}\sine{\left(x+\frac{\pi}{4}\right)}$
September22nd
When you multiply a vector by a scalar you have to multiply each component by the scalar
So it would be [15,-6]?
Ahhh
Thank you
It was the notations all along
I had a problem before that and I couldn’t figure it out so I clicked get a similar problem to try a different one and I kept running into the same problem so I started kinda guessing
Thanks Pali
Papi
Have a goodnight sleep tight so that the bed bugs don’t bite
that's kind of vague
weird way of phrasing it, but ok...
go a meters, turn around, go b meters, turn around again, go c meters
this is a - (b - c)
go a meters, go b meters backward, then go c meters
this is a - b + c
go a forward, then b backward, then c backward
"turn around" is more like -(...)
than just -
you could say that
thats a little trickier to get a visual for, i'm afraid
can you send a pic of the entire question
I would like to know the name of the book pls.
Calculus of a single variable,10th edition
Thanks
what you can do is get an expression for $$a_{n+1} - a_n$$
indolentbrains
indolentbrains
this will imply that {a_n} is a Cauchy sequence
having a bit of trouble here....
Hey if someone is available Friday to help me out with some hw pls DM me
@shell flicker I can help.
DM
I got (0,5) and this being a point of inflection, is this correct?
how would I determine whether its a point of max, min or inflection
well how did you get that it's a point of inflection?
was it a guess or did something make you conclude this?
I don't really know to be honest
so it was a guess?
sort of
there is no "sort of". if you can't explain what led you to the answer, it is as good as a guess.
in any case, you would look at the second derivative of your function at the stationary point.
f''(0), in your case.
so 0?
no, f''(0) ≠ 0 for your function.
is't f'(x) = -2x
that's the first derivative.
-2x+h
what is this?
refer to this message.
do you understand what a second derivative is?
no
did that never come up in your class?
did the concept of "take the derivative of the derivative" never earn so much as a passing mention by your teacher?
not sure, is there an equation for it?
the examples look like this
oh, so you were never told about it.
no
in that case, i suppose you are forced to consider the values of the first derivative at points near your stationary point, and see whether it is positive or negative
wait is it a max?
if it's the same sign on both sides, you have a point of inflection.
if it's negative to the left and positive to the right, you have a minimum.
if it's the other way around, you have a maximum.
yes, in your case you have a maximum.
Can cos(x) and cos(2x) be the same value?
yeah so I had a tan(x) = -sqrt(3) from pi/2 <x <pi
so doing math I found
sin(x) = sqrt(3)/2
cos(x) = -1/2
using cos(2x) = cos^(2)(x) - sin^(2)(x)
cos(2x) = (-1/2)^(2) - (sqrt(3)/2)^2
cos(2x) = 1/4 - 3/4
cos(2x) = -1/2
yes. In this case cos(120) = cos(240)
"a" is just another variable
m(a) means we substitute "a" in the place of x
m(a) = 2 is nothing but (a+1)/3 = 2
you can use this to solve for "a", same method for other sums
I can help you with it
opt a
aight man thanks guys
it was an exercise u cant just give an answer like that 
ok see, what this wants u to do is find values of x for which the function is equal to whatever is given,
like m(a)=2 basically means for which value of a
(a+1)/3=2
or in case of the other options, u will have to basically change the right side of the equation to whatever is given and solve it for a
np
hi
express sec in terms of cos
and then do common denominator for the expression in the numerator
and you should apply sum to prod formula
thanks i got the ans
Hey is proving things just trying valid operations and seeing if you're getting closer ?
Or is there some logic behind it
Also
I can't seem to prove this one, could someone maybe help ?
Convert all the cosine terms to sine
you could do it the teacher way with LHS and RHS
or change the statement to $sin^2x(cos^2y-1)+sin^2y(1-cos^2x) = 0$
Xiangli
would would be easier to prove.
can anyone help me with precal?
cashapp is an option, i have no idea how to do it rn
@visual birch don't offer cash for hw help
I would start with the left
Write cos ^ 2 y as 1- sin^2 y
Same for the cos^2 x
So now it’s sin^2x (1-sin^2y) - (1-sin^2x)(sin^2y)
So LHS= sin^2x -sin^2x sin^2y -sin^2y + sin^2xsin^2y
The sin^2xsin^y terms cancel
Leaving you with the RHS
"The distance between |x - 1| and 2 is greater than 2"
Which means that |x - 1| < 0 or |x - 1| > 4
@mental wedge
We can repeat the same logic. On the first equation:
"The distance between x and 1 is less than 0"
That's obviously impossible, there's no solutions there. What does it look like when applied to the second equation?
X, is either greater than 5 or lesser than minus 3??
Nailed it
Note that you can rewrite it as:
||x - 1| - (-2)| < 1
Oh... OK.
Hey, I found f'(x) for x ≠ 0 but I'm not sure how I would proceed to find f'(0) if it exists
(a/b)/c
= a/bc
a/(bc) but yes
using the limit definition
okay I'll try that thanks!
how would you solve this with the cauchy schwarz inequality?
let u = a+b, v = a+c, w = b+c, then a+b+c = 1/2 (u+v+w)
apply cauchy-schwarz to the vectors [sqrt(u), sqrt(v), sqrt(w)] and [1/sqrt(u), 1/sqrt(v), 1/sqrt(w)]
thanks!
I know part b is correct, but i’m unsure about c, it just doesn’t feel right i guess
why are you not using woflam alpha.
or you could just check it with your calculator
substitute B = arctan(40/9) + 180 and A = 180 - arcsin(7/25). Use your calculator to see if you got the angle additions correct
@flint bloom
dk why i didn’t think of that, i was treating A as 7/25 instead of the arcsin of that since A is an angle, it worked out correctly
Can someone help me out with basic pre-calculus? Pls ping m
just ask
you should and you are right, but I meant to check your answer, you would do it the arcsin way.
@tardy ridge
using the same way to check, the answer should be the positive version of this
i’m not sure why it’s coming out negative though
does it have to do with me checking it with arcsin
bc i checked with arccos and it comes out negative instead
ask your question
what is the menaing of dx/d?
do you mean d/dx
ahh yess
it’s the notation used which means to differentiate with respect to the variable, in this case, x
what is the meaning of this ∫ symbol?
to integrate, the opposite of a derivative
anti derivative
used to find areas or volumes
what are the variable we write on top and botton of ∫ ?
Why do we write those?
to show which section we want to take the area or volume of
it like tells us which region we are working with
Are those mandatory ?
no
we can have ∫ without anything above and below, it just means to take the anti derivative of the integrand
but with numbers we are gonna end up with a number at the end of it all
Can you give me an example on how to represent a derivative and an intergral?
put d/dx infront of a function of x
put a function of x after the integral symbol, and then a dx after the function
using k as the constant of proportionality, what does it mean if z is jointly proportional with w and u and is inversely proportional with p?
this was a question I was given, and I wasn't sure how to write out the equation.
should i read a book about precalc or no? i use khan academy is that enough?
z = kwu/p
ok, that makes sense
thanks for the help :)
For the sandwich theorem, is it correct to say that if the left and right sides of the inequality (in this case the functions f(x) and h(x)) give different values when applying the limit, then the limit for g(x) does not exist?
no, it's not.
if $f(x) \leq g(x) \leq h(x)$ but $\lim_{x \to c} f(x) \neq \lim_{x \to c} h(x)$, you cannot say $\lim_{x \to c} g(x)$ doesn't exist. after all, maybe it DOES exist, and you just picked a bad pair of bounding functions!
Ann
the squeeze theorem simply does not apply.
yes?
suppose i have limit (x tends to 1+) -(1+x) . cos(1/(1-x))
can I just directly say that the limit does not exist as I can't simplify it further?
$\lim_{x \to 1^+} -(x+1) \cos(\frac{1}{1-x})$
Ann
this?
yes
"as I can't simplify it further" is not good reason for the nonexistence of a limit.
true
so could I say it doesn't exist because I get 0 x cos (infinity) ?
I'm not sure how I can say the limit doesnt exist
you will not get 0 * cos(∞)
I incorrectly used the sandwich theorem to "prove" it prior to this
oh
anyway, to establish nonexistence, you could construct two sequences $x_n, y_n$ such that $x_n \to 1^+$ and $y_n \to 1^+$ but $\lim f(x_n) \neq \lim f(y_n)$
Ann
where f(x) is the stuff in your limit
ohh
reminds me of the method to prove whether a function is one-one or not
but i haven't been taught how to do that yet
by "that" i mean this
then i cannot help you
the negative answer is right.
are you sure you're using A = 180 - arcsin(7/25)
the angle is in the second quadrant.
do not use A = sin(7/25), that's the angle in the first quadrant.
What have you tried?
$\left(\frac{f}{g}\right)'=\frac{f'g-g'f}{g^2}$
Muzan Jackson
Does anyone know about the proof of this statement?
ty
@shell flickerso here was my thought process.
Assuming there isn't a horizontal shift in the entire function, I know that sin of zero is zero, meaning the sin function crosses the origin. Because this graph does, it's a sin function.
I also know that because the slope from x = [-pi,pi] is negative, that equation is going to have a negative in it.
This is where I combined luck and knowledge. So I know that B increases/decreases the period of a function. If you understand the unit circle or memorize how a sin wave moves in the real world, from the origin, it moves down and up to make a minimum, then goes up and passes the x axis and comes back down eventually to make a maximum. When it crosses the x axis again, it makes a full revolution (2pi).
This is longer than what the graph shows, as all is happening in the graph above is it's making a local maximum and passes 2pi at the x axis. The part where I got lucky was I set B to 1/2 and I imitated the graph shown on the screen. If you're not as lucky, there is a formula that would show you what B would be, but I don't remember that anymore.
Taking all those elements, the equation I got was -2sin.5(x)
The reason why it's 2 is because that's the amplitude, which is what the extrema are.
How do I graph a circle using this equation? I know the center radius one with h,k and r, but this isn't as obvious to me. I had a problem like this on a test I did a while back, and I didn't understand it at the time. I couldn't find many resources for this ether.
there should be plenty of resources for this
look up completing the square
and converting equation of a circle from general to standard form
I think I know how to complete the square. Is the standard form the name of the equation above?
the eqn you posted would be general form
different locations use the words general and standard differently
ah ok
you could call that center (-radius) form if you want
ok, I found some resources while finding out what the name was too. thx for the help :)
could someone please help me
no idea what I'm doing
also don't understand how its possible to evaluate trig functions with values greater than 90 lol
sry I'm stupid
so yeah
Thx
does this jog your mind?
Still need help with this
Are you asking me for help or if I need help?
Do you need help with the circle eq
Nah I think I got it
Just do completing the square twice to turn it to the other equation
K. Gg
Is this demonstration for the limit of x*sin(1/x) using the squeeze theorem accurate? I dont understand why you can multiply by x in the 1st line and maintain the inequality. Doesn't x have to be positive for that?
it holds for x>0; we can use it to squeeze the right side lim. we can write a similar inequality for x<0 that lets us squeeze the left side lim. then we have the 2 sided lim
oooooh thanks!
For #20 how do you set that up
you just have to integrate twice
why does the sign flip in this problem?
are you talking about the bit i highlighted in red?
well they tell you right here
they divide both sides of the ineq by -9, a negative number
so whenever you divide by a negative, you change the sign?
yes. whenever you divide both sides of an inequality by a negative number, the sign gets flipped.
ah ok, I didn't know that, thx for the help :)
i have a super simple problem that im not understanding why im getting the wrong answer
wouldnt we just be getting
e^ (delta v / ve) = ma/mf for the answer
i thought thatsd what it was, but using the given in #hint 1
this is wrong
$e^{\Delta v/v_e} = \frac{m_0}{m_f}$ is a step towards the solution but you aren't done yet
Ann
wym, dont i want that ratio
no, the proportion of fuel is $\frac{m_0 - m_f}{m_0}$
Ann
m0 = total, mf = payload
ohhhhh
how would i get to that equation from m0/mf
we arent given their individual values
@willow bear
consider: $\frac{m_0 - m_f}{m_0} = 1 - \frac{m_f}{m_0} = 1 - \paren{\frac{m_0}{m_f}}^{-1}$
Ann
thank you
can anyone help with question b
what is y in part a?
Once you found y in part a it's simple
Find the second derivative
Multiple both sides by x^2
Try to bring y in the right hand side
Your y should be x^2 + (3/x)
The second derivative should be 2 + (6/x^3)
ok @quick bluff thanks.
Having trouble applying compound interest formula. P = 10000 two different rates 3.5% monthly vs 6.5% quarterly for 10 years. I get 610,634 for the 3.5 and 114,160.75 for the 6.5. What am I doing wrong?
what you're doing wrong is having the entire annual rate get applied every month and quarter, respectively.
you probably calculated the first investment as $$10000 \cdot (1 + 0.035)^{12 \cdot 10},$$ didn't you?
Ann
@bleak cradle
I did. What should I have done?
you should've done $10000 \cdot \paren{1 + \frac{0.035}{12}}^{12 \cdot 10}$
Ann
Ahh. Let me try it again. Thank you.
when compounding several times a year, the annual interest rate gets spread out evenly over your compounding periods
Ok. I think I follow.
this applies to both your problems
Thank you so much.
<@&268886789983436800>
wow
Narcos
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Huh
Bruh
<@&268886789983436800> help plz ^^"
wow
seriously just what is the point
lol
i love having a name that starts with the letter A
Wtf is going on

What a weirdo
christ
that was terrible
ty
Why
nothing quite like it
smh~my head
the world is ending
kek
Mans def hates people with the letter A
who pinged
ping
at least the chat is finally active
ayo fuck u
glizzy time
pang
oh itachi's here
hm?
??
It’s chi
chat came back from the dead
lols im not even in precalc
whats up fellow As
who ping
lol all the A letter people have been united
precalc gang
Random user used: Summon
huh
sup!
Euler was wrong
someone pinged me
amogus
bruh

time to share our math memes and reminisce high school
I don't ave letter A

is this a smart people chat i might have to leave
and i dont even chat here
now that we have all been gathered here
everyone please chill
A GANG UNITE!!!!
i was chilling, then ping guy arrives
LMFAOO
lol
pre calc gang
Illegal
i dont even know pre calculus smh
Letter A mfs unite to destroy the pinger
y'all
wait what's goin on
packin
the hell
ikr
im just here for the emotes
me neither lmfaoo
massive ping
<@&268886789983436800>
@dark plank
begone
damn he got ass
ok we're on slowmode
th ot
Sigh
Back to my hole I go
dam
shitpost hours
YOoooooo
One is prime change my mind
for..?
also why slowmode if ping
ok this was nice cya
nah u wrong as hell
TF
how come i have pings turned off for this channel but i still got it
everyone stop shitposting
is this precalc??
whats with the shitposting at least make them good shitposts
for nothing, someone wanted to ping everyone haha

magic
1÷0=♾
damn yall really taking the chance]
who pinged me?

egg
yay its over
a spammer
cringe. maybe ping in general next time
who pinged me lmao
Didn't seem to work
🦦
@stuck lark just turn chatting in this channel off for 5-10 minutes
6 hr slowmode
Sorry
pornography
kek
6h slowmode petition
bruh im not smart
im not even in precalc:dead-4:
Lmao is some cunt with no life masspinging
aww it's not actually 6 hours
shamrock can you help me with vector fields
Manjaro sucks btw
wtf

oh nvm
btw staff here should change member perms lol?
Blocked
your os sucks btw
I'm freaking out over this ping, I can't continue my life, it's blocking my daily life man
i mildly dislike anime
any non precalc msgs will be met with mutes
Manjaro is based off Arch Linux and Arch Linux is the really thing 
who tagged
thanks for your valued opinion
to anyone wondering why they were pinged, there was a masspinging troll
Ok at least u like arch and not like macos or some shit
Yea build your own arch lmao
first mute
bruh I used to use my Hackintosh
guys move to another channel
i could say something in this channel, but if i got muted it would be a mute point
4th
heck i just wanted to continue this os talk in a different channel...
Is math analysis the same as precalculus if it is the name of the course you do right before calculus at my school?
you'd need to share parts of the curr
I was pinged yes
Who hath pinged me
I think some guy decided to just ping everyone alphabetically

What a legend
hmmm
Should I be terrified?
Did i get pinged
I did algebra 2/trig last year and it was mostly fine
Was it a mass ping
idk you as a math student
see the pins
bruh
Wacky
lot of people starting with 'a' and people with the honorable role. probably pinged everyone on the user list from top to bottom
Somehow i got pinged too
ah man I got pinged too and I thought someone finally solved the problem I asked like 2 months ago 😔
wtf ping?
:ping:
omg whoa okay that explains it
ping
lol i mean dont u like the little burst of dopamine, when you see that you got pinged because that means someone is paying attention to you and thinking of you, even though its an online stranger most likely? isnt that the reason you so readily came to this channel but then was dissapointed to find nobody of the sort?
i like not being pinged unless its important?
The 7th question, the answer given is option A
But according to my steps doesn't "a" have to be 4?
,rotate
:(
you're checking differentiability at a point so you will be taking the LHD and RHD at x=0 so you should replace x with 0 in your expression
cue the 10000000 clones of macos' ui done in different linux distros
why ping
who pung me
there was a mass pinger earlier
you would want to simplify this to an algebraic expression in x using the trigonometric identity 1+tan^2x=sec^2x , so you would want to do the substitution theta=arctan(x) and then proceed
The final simplification part was a bit confusing
But I think I solved it now
Thanks for your support :-)
sec(x)+tan(x)=tan(pi/4+x/2) iirc
I mean this is just chain rule , which is not incorrect but I think turning this problem into algebraic is more efficient and pretty standard , this works tho
Yep thanks for the help
not sure how to tackle this
find f^(-1) for that f(x)
then equate them and determine (a,b)
f^-1(x) would be x - b/ a, correct?
Mosh
Mosh
excuse me but wouldn't that be the same thing
(1/a) times x equals x/a
yeah.. not what you wrote
x/a - b/a because they have the same denominator would be x - b/ a
$x-\frac{b}{a}$ is what you wrote
Mosh
then yes
Mosh
so clearly you need a=1/a and b=-b/a
Part (A)
The answer is given as 4
My logic was the function becomes non differentiable everytime the mod switches signs
That is every time tan x = cot x after which the function changes
But I'm pretty sure it's wrong
I drew the graph of tan and cot and I see only three places where | tan x - cot x| would open with different signs
OH
WAIT
One sec
Lmao the graph is wrong
Oh wait
Technically all you need is to find the spot where f(x) is undefined and f'(x)is undefined
Because
- If the function is already undefined, how cna there be a rate of change anyway?
- Rate of change is undefined
Wait why does it need to be undefined?
Reasons are above
Not differentiable implies that the rate of change is undefined at some points
Or the limits dne
Isn't it not differentiable even if there's just a sharp turn?
That is, when the function changes?
Yes
Actually, i was wrong, scratch the first point
Okok
Oh wait lemme see
Waler could you verify one thing for me?
I think im confusing kyself with another fact here
Isn't this graph incorrect?
Oh yeah nvm, this is right
The dark lines are tan x and lighter ones are cot x
The function has to be defined first for it to be differentiable
Ill check
Pretty sure this is correct
I think I got it
Because tan x and cot x intersect 4 times between 0 and 2 pi
After which | tan x - cot x | will open with different signs
This changes the entire function giving it a sharp edge pretty sure
Am I right?
Yeah my brain is shitting itself lmfao
Is it the graph of |tanx -cotx| or graph of the given function
Ah
The dark lines are for tan x and the lighter ones are for cot x
Then yeah, seems good
Nono, actually...
Even that seems wrong 
Because there are like 6 regions where tan x and cot x switch in their magnitudes?
One sec
Im not sure what you mean
But the graph is correct
The two graphs should intersect at kpi/2 + pi/4
Split it into 8 regions
In the first region, cot x > tan x
2nd region, tan x > cot x
3rd region, cot x > tan x
And so on
Yep
So shouldn't it be 8 then?
8 what?
8 points where | tan x - cot x | opens differently
Thereby changing the entire function
Giving it 8 points of non differentiability?
Since its an oscillating function so yes
^
That was a different problem
This discussion was entirely for part A of this question right?
Oh wait qctually
When the mod opens with +ve, the function is cot x, when it opens with -ve, the function is tan x
The opening of the mod changes only when tan x > cot x switches to cot x > tan x or vice versa
From here I'm able to see 8 places where the opening of the mod changes
No no, i have mistkaen
Oh
The sign only changes when tanx -cotx equates 0
Is this wrong?
Lemme just draw it out
Okok
Disregard this
This is the graph of the asb value function
The red is the graph
Dotted red is the mirror of the bpue portion
Hmm wait a min
Kk
Im not sure how to explane this
My issue right now is by my logic the answer should be 8
But it's flawed somehow and I don't know where
Ok so basically
Ye
lets take it easy, and consider tanx - cotx
Kk
This is the graph of tanx and cotx
Yes
You will see that they have x ints every kpi/2 + pi/4
(Basically where tanx and cotx intersect)
Yes
And is negative in portion 1, 3, 5 and 7
Oh
This is the graph of tan x - cot x?
Yep
Oh kk
So now when applying the absolute value to it
We want to mirror the negative portion of the graph
Yes
Yes
Lmao np
Basically now you notice that these "sharp turns" exists at points where |f(x)|=0
Yes
Or simply put f(x)=0
Yup
Which there exists to be 4

Huh, i just realised that, the sharp turns are always at the x-int
Alright thats cool
New knowledge obtained
Alright, now there's this one final doubt
when i actually graph it out
OHH NVM
NVM
lmao
Yeah seems logical
the question states points where they are "continuous and undifferentiable"
Thanks a lot dude
👍
is $\frac{1-\sqrt{x}+x\sqrt{x}}{x}$ the same as $\sqrt{x}$?
Pahul's Uncle
clearly it's not since the graphs are different when i check on desmos but when I try simplifying they are the same
im not sure why
im probably simplifying wrong
but the textbook answer key says the continous interval is x>0 which led me to believe that it was indeed the same as sqrt(x)
i think i know why you got $\sqrt{x}$, but the numerator simplifies as $\sqrt{x}(x-1)+1$, not $\sqrt{x}(x-1+1)$
mchen10
my algebra skills are wack
can you explain a bit more
maybe the steps
i cant get it to simplify to $\sqrt{x}(x-1)+1$
Pahul's Uncle
ok
thanks
np
not every function continuous only on the positive axis is sqrt(x) 
yeah but i figured I was on the right track
obviously I wasnt
s l o p e
also this might help you;
as r->0, ab becomes perpendicular to y axis
so center-c becomes (inf, 0)
it basically diverges to nigh
oh well bye
Is this correct?
Looks right to me
Thank you
If you want to just derive the functions, which I think you do
Yes
Thought that we couldn't directly derive each function within individually for some reason
Thanks again 
The 12th question
I'm able to say f(x) is continuous by using the sandwich theorem
But I'm not sure how I can tell anything about f(x)'s differentiability at x=0
Take f(x) =x^2
What does |f(x)| imply? Does it imply we can access the negative range values as well?
The answer should be option 3, if my earlier statement holds true. We get two graphs, and origin act as a mirror for x^2.
Yes, the answer given is option 3
But how can we take f(x) as x^2 itself?
Is it becausef(x) and x^2 more or less become the same when tending to 0?
X^2 full fill all the conditions
Can you tell me when does a function become non-differentiable?
When it's not continuous or when the derivative is infinite or when the left and right hand derivatives don't match up?
Sure. You are right! If the function is discontinuous at point P, it will be non-differentiable at P(--temporary--). And, at sharp corners, it is non-differentiable too. That sentence is an underestimation. We should rather say, at sharp corners, the function becomes enormously differentiable. So much so that at one specific point, we get multiple distinct values of the derivative.
Is this statement incorrect?
I am not sure what you mean, but probably you are misinterpreting it. Think of x^2 as a function (which it is) and it is = f(x). They both affect each other. Guess the value of x and you will get f(x). At 0, yes, they converge to a specific number which is 0. But you will notice that |f(x)| is not a function, which I guess you can make sense of (or feel free to ask).
Also, remember this - Tangent is not the same thing as derivative. If f(x) is a function then at point x0 its derivative is f'(x0), which is the slope of the tangent line to f(x) at point P. At a sharp point, we get multiple tangents. It implies there have to be multiple slopes, which in turn means distinct derivates.
Having additional knowledge doesn't hurt. I was trying to give a conceptual and clear understanding,
Ah yes, I keep confusing derivatives as the tangents themselves instead of the slope of the tangents
Suppose the inequality was just < and not <=, would I still be able to take |f(x)| as x^2?
That's a naive statement. We should never just say a function is continuous or discontinuous. We MUST always mention the bounds (or the domain) while mentioning continuity or discontinuity. Ex - Every discontinuous function can be continuous for some ∂≈0.
It is not about seeing the applicability of some theorems. One should get a sense of whatever is going on.
So when I remove the = from <= in the question, I can't tell anything about it's continuity since f(x) might be close to the upper and lower bounds (x^2 and -x^2) or f(x) might not be near them at all?
Oh wait
When I reread what I wrote it makes no sense 
Yes, it doesn't make sense because I didn't mention for which domain I'm checking the continuity for? 
One thing that helps me a lot in mathematics is to frame a literature sense of the equation. I would recommend you do that as well. Ex: y < x. Mathematically : y < x. Literature wise - "So, it is saying we have to find all those x's that are bigger than y. But where can Y = X? oh, it's that y = x line. Below it, x > all y's and above it y > all x's." That's one way to solve things in math. Step by step from the ground up.
Noted, I'll try my best to implement this into my thinking process
OH WAIT
I think I got something
f is from R to R
So every input x HAS to give an output
When u graph out the upper and lower bounds
That is x^2 and -x^2
They have a common tangent at x=0
And since f(x) lies between x^2 and -x^2
It has to pass through this point with the same slope?

I think the mistake I have been making is trying to look at f(x)'s behaviour at all R instead of just around x=0
Exactly! But a little correction in your above statement. It should be f(x) is = x^2 and f(x) = -x^2 simultaneously. It would lie between them when there's just "< or >" inequality.
Oh yes
And, since |f(X)| has two different simultaneous outputs (x^2, and -x^2), that is why it is NOT a function.
Makes sense
Yeah I think I get what you and learn4math were telling me now 
Thanks a lot! 
JEE is doable. All you need is an enthusiastic teacher (who can extend equations to real life applications) and a passion ingrained in you.
I have the enthusiastic teachers, searching for the passion
This is dumb but how can I simplify 4^2^x
Mosh
The second one sorry
it cant be as far as I'm aware
Actually like 2^(2^(2x+1))
ok yeah, $2^{2\cdot 2^x}=2^{2^{x+1}}$
Mosh
Is there anything else that can be done
not really
The 14th sum
Answer is given as option 2
Sending some steps, one sec
I'm getting the answer but I'm pretty sure my reasoning is incorrect
From the first statement
I substituted x = 0
f'(0) give -1 and 1 respectively
f'(f(0)) give values -cos(ln2) and cos(ln2) respectively
Can I multiply the pairs of values of f'(0) and f'(f(0)) and conclude that since both of them give the value cos(ln2), g'(0) is cos(ln2) ?
i mean that's okay, but when finding the piecewise function, as you are asked at x=0, you can perfectly plug it into ln(2)≥sin(x) and ln(2)<sin(x) and see which one is true, and then go with that one instead of doing both values
OHH
So at x = 0 only ln(2) > sin(0) is true so I can ignore the function in the interval ln(2)<sin(x) ?
pretty much, yeah. piecewise functions are made so that when working with a certain point, you'd want the part of the piecewise functions that corresponds to that interval.
Thanks a lot 
The way you wrote f'(x) after f'(f(x)) is quite astonishing.
Wait does it look weird?
is it? all they did was apply the chain rule
Or did I make a mistake of some sort?
It is not weird. Rather a notational abuse I would say. f(x) is not differentiable(at a lot of points), so I am not sure what you are going to get by f'(x).
But isn't it differentiable around 0?
The options make it clear that they want us to check the differentiability at 0 I'm pretty sure
It sure is differentiable around 0. I am speaking in general and I have seen people taking such a path with the composition rule of differentiation (chain rule) where they might differentiate the inner function without realizing whether it is differentiable or not.
I mean we have a rule(chain rule), and that is fine. But we must understand the kind of functions(and domains) we are dealing with. It is such a subtle thing I guess.
In this case? No. Can it be wrong in othe case? Maybe.
abovewater i think you're being a little pedantic here
Ironically, limit is about being precise with the degree of approximations we are making. I am just trying to give him a different lens to look through.
A new word has been added to my vocabulary 
Is the reasoning correct? The question was to find K which is the set of all points where f(x) is not differentiable
Paradon me but I am having trouble reading your handwriting. From what I can barely make, it seems correct.
What is this font lmao
no, because youre taking the derivative with x in the exponent, so the power rule doesn't apply
the derivative of e^x is e^x, but you need to use the chain rule
$\frac{d}{dx}e^{\frac{x}{2}}=\frac{1}{2}e^{\frac{x}{2}}$
mchen10
im confused
the book didnt give me any tips
ffs
like it gave me some formulas, i thought i was supposed to follow them
the book gave me this
i see nothing here that can help with this scenario besides the e^x
do you?
mchen10
sorry had to go
but can you explain that ?
a bit confused how you got there
the derivative of e^kx is in your book, but basically the derivative of f(g(x)) is f'(g(x)) * g'(x), which is also called the chain rule
Well here is the weird thing
the book teaches the chain rule a bit further up
where im at
its before chain rule
which is weird why the book would expect me to know that
i guess they just want you to use the formula first
ok so i should learn the chain rule then get back to the question?
so you didnt use the e^kx to solve the question?
i did. the book says $\frac{d}{dx}e^{kx}= ke^{kx}$, so i just plugged in k=1/2 to get the answer
mchen10
you wanted to find the derivative of $e^{\frac{x}{2}}$, so that's just what i did
mchen10
$\frac{x}{2}=\frac{1}{2}x$
mchen10
are these logs meant to be decimal logs or natural logs?
just natural
natural, ok
note that any solution to this must be greater than 21 (otherwise log(x-21) is undefined!)
and after doing so, take e^(both sides)
then I simplify and find the 2 x values
what you should end up with is an equation without logarithms, which you will then solve as normal
and then, once you've got your x values, you check them against the condition x > 21
Because it's a perfect square?
ty
How do we know that?
(ax - b)^2 is (ax - b)(ax - b)
How does this immediately lead to a discriminant of 0?
How do I not see this?
OHHHH
Only one solution for x
If f(x) = 0
yep
Not sure how I can proceed from here or if there's a simpler method
The question actually asks for y'(1)
before heading onto that, the derivative of x^(2x) and x^x aren't correct, you can't differentiate these like you would with x^2 for example.
I should use the chain rule right?
uh yeah, but still that's not how you'd differentiate these.
you can consider e^ln(x)=x for example.
so that $\overbrace{{\color{green}{x}}^{x}}^{{\color{green}{x}}=e^{\ln( {\color{green}{x}} )}}= \left(e^{\ln( {\color{green}{x}} )}\right)^x=e^{x\ln(x)}$
Ok
Al𝟛dium
so basically I try to convert these functions into known functions by taking ln?
kind of yeah, you are essentially manipulaying x^x so that it becomes an easier function to differentiate.
Would it be correct if I take both negative terms to the RHS and take ln on both sides and then differentiate?
Ah I see
do you mean from the very beginning?
Yes
yeah you perfectly could.
so that's up to you
makes sense
