#precalculus

1 messages · Page 293 of 1

restive bridge
#

Desmos I thought was just for graphing

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good to know there's more to it

willow bear
#

$\sin(2\theta) = 2\sin(\theta)\cos(\theta)$

obsidian monolithBOT
willow bear
#

also consider $(\cos(\theta) + \sin(\theta))^2$

obsidian monolithBOT
willow bear
#

@viscid thistle

ancient rampart
#

are 2 vectors considered parllel if they are like on top of each other

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for example <2, -1> and <4, -2>

mild swan
#

I would argue yes

sick steppe
finite birch
#

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:)

tardy ridge
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How do I represent 2 equations into a parametric equation

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like -4x-6y+3z-6=0

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and 3x+2y+4z+2=0

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nevermind I got it

frigid sonnet
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can some one break this down please

uncut mulch
#

its notation for function compositions

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eg.
(fog)(x) = f(g(x))

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which you should know how to do with a basic understanding of function notation

visual brook
tardy ridge
#

wut

rigid beacon
#

I've never heard that term before

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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

stable crown
#

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 = $(\pi n+tan^{-1} (\frac{1}{5}(3-\sqrt(14)))$ ; $n \me \mathbb{Z}$

obsidian monolithBOT
#

Panic Of Kernel
Compile Error! Click the errors reaction for more information.
(You may edit your message to recompile.)

willow bear
#

$\theta = \pi n + \tan^{-1}\left(\frac{1}{5}(3 - \sqrt{14})\right), n \in \mathbb{Z}$

obsidian monolithBOT
willow bear
#

@stable crown fixed that tex for you

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but also you don't need this lol

barren hatch
#

Could I get some help?

willow bear
#

with what?

visual brook
#

Just do $\sine{x}+\cosine{x}=\sqrt{2}\sine{\left(x+\frac{\pi}{4}\right)}$

obsidian monolithBOT
#

September22nd

barren hatch
#

Vectors

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@willow bear

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I have a pic sending

visual brook
#

Can you send your q instead of saying you need help

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Okay

barren hatch
#

See it??

visual brook
#

When you multiply a vector by a scalar you have to multiply each component by the scalar

barren hatch
#

So it would be [15,-6]?

visual brook
#

Yes

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But use the <> notation

barren hatch
#

Ahhh

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Thank you

#

It was the notations all along

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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

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Thanks Pali

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Papi

visual brook
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Uhhh

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No problem

barren hatch
#

Have a goodnight sleep tight so that the bed bugs don’t bite

willow bear
#

that's kind of vague

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weird way of phrasing it, but ok...

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go a meters, turn around, go b meters, turn around again, go c meters

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this is a - (b - c)

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go a meters, go b meters backward, then go c meters

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this is a - b + c

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go a forward, then b backward, then c backward

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"turn around" is more like -(...)

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than just -

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you could say that

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thats a little trickier to get a visual for, i'm afraid

fickle steeple
#

Can someone please help in solving this question

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Feel free to DM if you like

tranquil lava
#

can you send a pic of the entire question

fickle steeple
#

Sure

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Q.no.86

stable crown
fickle steeple
#

Calculus of a single variable,10th edition

stable crown
#

Thanks

tranquil lava
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what you can do is get an expression for $$a_{n+1} - a_n$$

obsidian monolithBOT
#

indolentbrains

tranquil lava
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for part a

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or an expression for $$\frac{a_{n+1}}{a_n}$$

obsidian monolithBOT
#

indolentbrains

tranquil lava
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this will imply that {a_n} is a Cauchy sequence

near epoch
#

having a bit of trouble here....

shell flicker
#

Hey if someone is available Friday to help me out with some hw pls DM me

vivid moth
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@shell flicker I can help.

shell flicker
outer inlet
#

I got (0,5) and this being a point of inflection, is this correct?

willow bear
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no

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the point itself is correct but your judgment of its type is not

outer inlet
#

how would I determine whether its a point of max, min or inflection

willow bear
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well how did you get that it's a point of inflection?

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was it a guess or did something make you conclude this?

outer inlet
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I don't really know to be honest

willow bear
#

so it was a guess?

outer inlet
#

sort of

willow bear
#

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.

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f''(0), in your case.

outer inlet
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so 0?

willow bear
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no, f''(0) ≠ 0 for your function.

outer inlet
#

is't f'(x) = -2x

willow bear
#

that's the first derivative.

outer inlet
#

-2x+h

willow bear
#

what is this?

outer inlet
#

idk

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I am lost

willow bear
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do you understand what a second derivative is?

outer inlet
#

no

willow bear
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did that never come up in your class?

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did the concept of "take the derivative of the derivative" never earn so much as a passing mention by your teacher?

outer inlet
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not sure, is there an equation for it?

willow bear
#

.......

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take the derivative of the derivative

outer inlet
#

the examples look like this

willow bear
#

oh, so you were never told about it.

outer inlet
#

no

willow bear
#

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

outer inlet
#

wait is it a max?

willow bear
#

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.

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yes, in your case you have a maximum.

outer inlet
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oh ok now I see it

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I drew the wrong diagram on my paper

edgy blaze
#

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

tardy ridge
viscid thistle
#

I need help with this problem

molten garnet
#

sonmeone help me with functions

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I hv no idea what a refers to

quick bluff
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"a" is just another variable

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m(a) means we substitute "a" in the place of x

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m(a) = 2 is nothing but (a+1)/3 = 2

quick bluff
viscid thistle
#

I can help you with it

viscid thistle
molten garnet
#

aight man thanks guys

brazen marsh
brazen marsh
# molten garnet

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

viscid thistle
#

Ok @brazen marsh ?

brazen marsh
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Oh i didnt read that

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sorry

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mb

viscid thistle
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np

plush copper
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hi

wary mulch
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idk how to do this sum

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if anyone is willing to help me pls mention me

trim hemlock
#

express sec in terms of cos

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and then do common denominator for the expression in the numerator

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and you should apply sum to prod formula

wary mulch
#

thanks i got the ans

tranquil haven
#

Hey is proving things just trying valid operations and seeing if you're getting closer ?

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Or is there some logic behind it

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Also

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I can't seem to prove this one, could someone maybe help ?

blissful ridge
#

Convert all the cosine terms to sine

tardy ridge
#

you could do it the teacher way with LHS and RHS

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or change the statement to $sin^2x(cos^2y-1)+sin^2y(1-cos^2x) = 0$

obsidian monolithBOT
#

Xiangli

tardy ridge
#

would would be easier to prove.

visual birch
#

can anyone help me with precal?

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cashapp is an option, i have no idea how to do it rn

tardy ridge
#

why would you pay them

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just ask the question here

stuck lark
#

@visual birch don't offer cash for hw help

rough carbon
# tranquil haven

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

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The sin^2xsin^y terms cancel

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Leaving you with the RHS

mental wedge
#

How do I solve the 7 and 8 sums??

patent beacon
#

"The distance between |x - 1| and 2 is greater than 2"

Which means that |x - 1| < 0 or |x - 1| > 4

mental wedge
#

Ye i got till this much

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Wats not??

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Nxt*

patent beacon
#

@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?

mental wedge
#

X, is either greater than 5 or lesser than minus 3??

patent beacon
#

Nailed it

mental wedge
#

Ig, IDK this is all new for me....

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Thnx

mental wedge
#

@patent beacon

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Wat abt the second one??

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The eighth question

patent beacon
tranquil haven
#

Is it allowed to rewrite a/b/c as a/bc ? If so, why ?

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Nevermind I understand it

willow bear
#

what do you mean by a/b/c?

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do you mean (a/b)/c or a/(b/c)? these are not the same

raven fulcrum
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Hey, I found f'(x) for x ≠ 0 but I'm not sure how I would proceed to find f'(0) if it exists

tranquil haven
#

= a/bc

willow bear
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a/(bc) but yes

raven fulcrum
#

okay I'll try that thanks!

simple parcel
#

how would you solve this with the cauchy schwarz inequality?

willow bear
#

let u = a+b, v = a+c, w = b+c, then a+b+c = 1/2 (u+v+w)

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apply cauchy-schwarz to the vectors [sqrt(u), sqrt(v), sqrt(w)] and [1/sqrt(u), 1/sqrt(v), 1/sqrt(w)]

simple parcel
#

thanks!

flint bloom
#

,rotate

obsidian monolithBOT
flint bloom
#

I know part b is correct, but i’m unsure about c, it just doesn’t feel right i guess

tardy ridge
#

why are you not using woflam alpha.

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or you could just check it with your calculator

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substitute B = arctan(40/9) + 180 and A = 180 - arcsin(7/25). Use your calculator to see if you got the angle additions correct

viscid thistle
tardy ridge
#

@flint bloom

flint bloom
viscid thistle
#

Can someone help me out with basic pre-calculus? Pls ping m

flint bloom
#

just ask

tardy ridge
flint bloom
#

@tardy ridge

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using the same way to check, the answer should be the positive version of this

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i’m not sure why it’s coming out negative though

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does it have to do with me checking it with arcsin

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bc i checked with arccos and it comes out negative instead

dire lintel
#

Can someone help me out with calculus?

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like the basic

flint bloom
#

ask your question

dire lintel
#

what is the menaing of dx/d?

flint bloom
#

do you mean d/dx

dire lintel
#

ahh yess

flint bloom
#

it’s the notation used which means to differentiate with respect to the variable, in this case, x

dire lintel
#

what is the meaning of this ∫ symbol?

flint bloom
#

to integrate, the opposite of a derivative

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anti derivative

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used to find areas or volumes

dire lintel
#

what are the variable we write on top and botton of ∫ ?

flint bloom
#

they can be variables but are mostly numbers

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they are the bounds

dire lintel
#

Why do we write those?

flint bloom
#

to show which section we want to take the area or volume of

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it like tells us which region we are working with

dire lintel
#

Are those mandatory ?

flint bloom
#

no

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we can have ∫ without anything above and below, it just means to take the anti derivative of the integrand

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but with numbers we are gonna end up with a number at the end of it all

dire lintel
#

Can you give me an example on how to represent a derivative and an intergral?

flint bloom
#

put d/dx infront of a function of x

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put a function of x after the integral symbol, and then a dx after the function

dire lintel
#

Oh k

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thank you

merry chasm
#

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.

cyan glacier
#

should i read a book about precalc or no? i use khan academy is that enough?

merry chasm
#

ok, that makes sense

thanks for the help :)

quick bluff
#

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?

willow bear
#

no, it's not.

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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!

obsidian monolithBOT
willow bear
#

the squeeze theorem simply does not apply.

quick bluff
#

thonk makes sense

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wait i have another doubt

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one sec

willow bear
#

yes?

quick bluff
#

suppose i have limit (x tends to 1+) -(1+x) . cos(1/(1-x))

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can I just directly say that the limit does not exist as I can't simplify it further?

willow bear
#

$\lim_{x \to 1^+} -(x+1) \cos(\frac{1}{1-x})$

obsidian monolithBOT
willow bear
#

this?

quick bluff
#

yes

willow bear
#

"as I can't simplify it further" is not good reason for the nonexistence of a limit.

quick bluff
#

true

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so could I say it doesn't exist because I get 0 x cos (infinity) ?

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I'm not sure how I can say the limit doesnt exist

willow bear
#

you will not get 0 * cos(∞)

quick bluff
#

I incorrectly used the sandwich theorem to "prove" it prior to this

quick bluff
willow bear
#

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 $\lim f(x_n) \neq \lim f(y_n)$

obsidian monolithBOT
willow bear
#

where f(x) is the stuff in your limit

quick bluff
#

ohh

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reminds me of the method to prove whether a function is one-one or not

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but i haven't been taught how to do that yet

quick bluff
willow bear
#

then i cannot help you

quick bluff
#

oh you have already helped me SO much

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thanks a lot Ann

tardy ridge
#

are you sure you're using A = 180 - arcsin(7/25)

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the angle is in the second quadrant.

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do not use A = sin(7/25), that's the angle in the first quadrant.

viscid thistle
trim hemlock
#

What have you tried?

warm forum
obsidian monolithBOT
#

Muzan Jackson

mortal iron
mortal iron
#

ty

shell flicker
#

Anyone know how to do this?

merry chasm
#

@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.

uncut mulch
#

there should be plenty of resources for this

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look up completing the square

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and converting equation of a circle from general to standard form

merry chasm
#

I think I know how to complete the square. Is the standard form the name of the equation above?

uncut mulch
#

the eqn you posted would be general form

merry chasm
#

🤔

#

this shit is giving me mixed messages

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@uncut mulch

uncut mulch
#

different locations use the words general and standard differently

merry chasm
#

ah ok

uncut mulch
#

you could call that center (-radius) form if you want

merry chasm
#

ok, I found some resources while finding out what the name was too. thx for the help :)

near epoch
#

could someone please help me

#

no idea what I'm doing

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also don't understand how its possible to evaluate trig functions with values greater than 90 lol

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sry I'm stupid

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so yeah

merry chasm
near epoch
#

@merry chasm thx but someone helped me

#

already

merry chasm
fleet yew
#

Do you need help with the circle eq

merry chasm
#

Nah I think I got it

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Just do completing the square twice to turn it to the other equation

fleet yew
#

K. Gg

cunning hollow
#

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?

stuck lark
viscid thistle
#

For #20 how do you set that up

trim hemlock
#

you just have to integrate twice

merry chasm
#

why does the sign flip in this problem?

willow bear
#

are you talking about the bit i highlighted in red?

merry chasm
#

yea

#

@willow bear

willow bear
#

well they tell you right here

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they divide both sides of the ineq by -9, a negative number

merry chasm
#

so whenever you divide by a negative, you change the sign?

willow bear
#

yes. whenever you divide both sides of an inequality by a negative number, the sign gets flipped.

merry chasm
#

ah ok, I didn't know that, thx for the help :)

vapid torrent
#

i have a super simple problem that im not understanding why im getting the wrong answer

#

wouldnt we just be getting

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e^ (delta v / ve) = ma/mf for the answer

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i thought thatsd what it was, but using the given in #hint 1

#

this is wrong

willow bear
#

$e^{\Delta v/v_e} = \frac{m_0}{m_f}$ is a step towards the solution but you aren't done yet

obsidian monolithBOT
vapid torrent
#

wym, dont i want that ratio

willow bear
#

no, the proportion of fuel is $\frac{m_0 - m_f}{m_0}$

obsidian monolithBOT
willow bear
#

m0 = total, mf = payload

vapid torrent
#

ohhhhh

#

how would i get to that equation from m0/mf

#

we arent given their individual values

#

@willow bear

willow bear
#

consider: $\frac{m_0 - m_f}{m_0} = 1 - \frac{m_f}{m_0} = 1 - \paren{\frac{m_0}{m_f}}^{-1}$

obsidian monolithBOT
vapid torrent
#

thank you

viscid thistle
#

can anyone help with question b

trim hemlock
#

what is y in part a?

quick bluff
#

Find the second derivative

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Multiple both sides by x^2

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Try to bring y in the right hand side

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Your y should be x^2 + (3/x)

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The second derivative should be 2 + (6/x^3)

viscid thistle
#

ok @quick bluff thanks.

bleak cradle
#

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?

willow bear
#

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?

obsidian monolithBOT
willow bear
#

@bleak cradle

bleak cradle
#

I did. What should I have done?

willow bear
#

you should've done $10000 \cdot \paren{1 + \frac{0.035}{12}}^{12 \cdot 10}$

obsidian monolithBOT
bleak cradle
#

Ahh. Let me try it again. Thank you.

willow bear
#

when compounding several times a year, the annual interest rate gets spread out evenly over your compounding periods

bleak cradle
#

Ok. I think I follow.

willow bear
#

this applies to both your problems

bleak cradle
#

Thank you so much.

jaunty thistle
#

Omg

#

hilarious

past meadow
#

<@&268886789983436800>

worldly badger
#

wow

obsidian monolithBOT
#

Narcos
Compile Error! Click the errors reaction for more information.
(You may edit your message to recompile.)

steep sinew
#

Huh

crimson magnet
#

Bruh

worldly badger
#

<@&268886789983436800> help plz ^^"

rain tide
#

wow

pastel jay
#

seriously just what is the point

golden flume
white thicket
#

lol

jagged violet
#

i love having a name that starts with the letter A

proper pendant
#

Wtf is going on

severe verge
viscid thistle
#

What a weirdo

orchid nova
#

christ

rain tide
#

that was terrible

stuck lark
#

ty

jaunty thistle
#

Why

jagged violet
#

nothing quite like it

digital kestrel
#

smh~my head

rain tide
#

the world is ending

twin escarp
#

kek

crimson magnet
#

Mans def hates people with the letter A

keen parrot
#

who pinged

pure light
#

ping

frank spruce
#

at least the chat is finally active

karmic burrow
#

ayo fuck u

twin escarp
#

glizzy time

rain tide
#

pang

digital kestrel
tender wigeon
#

hm?

misty bay
#

??

crimson magnet
#

It’s chi

digital kestrel
#

chat came back from the dead

tender wigeon
#

lols im not even in precalc

pure vine
#

whats up fellow As

wet remnant
#

who ping

white thicket
#

lol all the A letter people have been united

knotty spear
#

stare precalc gang

steep sinew
#

Random user used: Summon

wet oar
#

huh

pale geyser
#

sup!

lament radish
#

Euler was wrong

lilac marsh
#

someone pinged me

frail steppe
#

amogus

pure light
#

bruh

whole flint
frank spruce
#

time to share our math memes and reminisce high school

viscid thistle
#

I don't ave letter A

raven burrow
tender wigeon
#

is this a smart people chat i might have to leave7acosp_ummmwary

lilac marsh
#

and i dont even chat here

pure vine
#

now that we have all been gathered here

stuck lark
#

everyone please chill

wet remnant
#

A GANG UNITE!!!!

worldly badger
#

i was chilling, then ping guy arrives

tender wigeon
#

LMFAOO

worldly badger
#

lol

wet oar
#

pre calc gang

lime tusk
#

Illegal

pastel jay
#

i dont even know pre calculus smh

karmic burrow
#

Letter A mfs unite to destroy the pinger

digital kestrel
#

y'all

tender wigeon
#

wait what's goin on

plush birch
#

packin

digital kestrel
#

the hell

lilac marsh
viscid thistle
#

im just here for the emotes

tender wigeon
knotty spear
worldly badger
viscid thistle
#

<@&268886789983436800>

rain tide
#

@dark plank

knotty spear
#

begone

tender wigeon
#

damn he got ass

stuck lark
#

ok we're on slowmode

lilac marsh
rare nebula
#

Sigh

steep sinew
#

Back to my hole I go

plush birch
#

dam

karmic burrow
#

shitpost hours

wet oar
#

YOoooooo

lament radish
#

One is prime change my mind

tender wigeon
white thicket
#

ok this was nice cya

plush birch
wet oar
#

TF

viscid thistle
#

how come i have pings turned off for this channel but i still got it

stuck lark
#

everyone stop shitposting

sturdy relic
#

is this precalc??

frail steppe
pastel jay
#

whats with the shitposting at least make them good shitposts

worldly badger
opal veldt
viscid thistle
#

1÷0=♾

lilac marsh
#

damn yall really taking the chance]

maiden smelt
#

who pinged me?

tulip prism
frail steppe
#

egg

pastel jay
#

yay its over

worldly badger
tender wigeon
#

cringe. maybe ping in general next time

viscid thistle
#

who pinged

cursive fiber
#

who pinged me lmao

static reef
frail steppe
#

🦦

steep sinew
#

@stuck lark just turn chatting in this channel off for 5-10 minutes

viscid thistle
#

6 hr slowmode

lime tusk
frail steppe
#

pornography

orchid nova
pastel jay
#

6h slowmode petition

tender wigeon
boreal pumice
#

Lmao is some cunt with no life masspinging

orchid nova
#

aww it's not actually 6 hours

viscid thistle
#

shamrock can you help me with vector fields

knotty bane
viscid thistle
tender wigeon
#

wtf
dead dead dead
oh nvm
btw staff here should change member perms lol?

boreal pumice
pastel jay
viscid thistle
#

I'm freaking out over this ping, I can't continue my life, it's blocking my daily life man

stuck lark
#

anyone who wants to chill go to #chill

frail steppe
#

i mildly dislike anime

stuck lark
#

any non precalc msgs will be met with mutes

viscid thistle
lapis girder
#

who tagged

pastel jay
#

thanks for your valued opinion

stuck lark
#

to anyone wondering why they were pinged, there was a masspinging troll

boreal pumice
viscid thistle
stuck lark
#

first mute

viscid thistle
pastel jay
#

guys move to another channel

stuck lark
#

2nd mute

#

3rd mute

frail steppe
#

i could say something in this channel, but if i got muted it would be a mute point

stuck lark
#

4th

pastel jay
stuck lark
#

i'll say again. offtopic convos should be moved to #chill

lime tusk
#

Is math analysis the same as precalculus if it is the name of the course you do right before calculus at my school?

sick steppe
ivory needle
#

I was pinged yes

raw orbit
#

Who hath pinged me

ivory needle
#

I think some guy decided to just ping everyone alphabetically

raw orbit
sick steppe
#

yeah looks like it's just precalc

#

w/ first bit of regular calc 1

lime tusk
#

hmmm
Should I be terrified?

grizzled orchid
#

Did i get pinged

lime tusk
#

I did algebra 2/trig last year and it was mostly fine

grizzled orchid
#

Was it a mass ping

sick steppe
#

catshrug idk you as a math student

lime tusk
opaque belfry
#

bruh

grizzled orchid
#

Wacky

charred frigate
#

lot of people starting with 'a' and people with the honorable role. probably pinged everyone on the user list from top to bottom

viscid thistle
#

Somehow i got pinged too

toxic karma
#

ah man I got pinged too and I thought someone finally solved the problem I asked like 2 months ago 😔

ivory ravine
#

wtf ping?

versed escarp
#

:ping:

proud sparrow
viscid thistle
#

ping

viscid thistle
# ivory ravine wtf 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?

ivory ravine
quick bluff
#

The 7th question, the answer given is option A

#

But according to my steps doesn't "a" have to be 4?

past meadow
obsidian monolithBOT
past meadow
#

:(

golden latch
quick bluff
#

OHH

#

Thanks again

crimson steppe
misty hemlock
#

why ping

viscid thistle
#

who pung me

past meadow
#

there was a mass pinger earlier

agile nest
#

Can someone differentiate this?

golden latch
# agile nest

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

agile nest
#

The final simplification part was a bit confusing

#

But I think I solved it now

#

Thanks for your support :-)

golden latch
#

sec(x)+tan(x)=tan(pi/4+x/2) iirc

agile nest
#

I solved till this

golden latch
#

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

agile nest
#

Yep thanks for the help

viscid thistle
#

not sure how to tackle this

sick steppe
#

then equate them and determine (a,b)

viscid thistle
#

f^-1(x) would be x - b/ a, correct?

sick steppe
#

no

#

$x=ay+b$

obsidian monolithBOT
viscid thistle
#

oh right

#

oops

#

wait but then

#

when you isolate y

#

it's x - b/ a right?

sick steppe
#

no

#

$y=\frac{1}{a}(x-b)=\frac{1}{a}x-\frac{b}{a}$

obsidian monolithBOT
viscid thistle
#

excuse me but wouldn't that be the same thing

sick steppe
#

no..

#

1/a clearly isnt 1

viscid thistle
#

(1/a) times x equals x/a

sick steppe
#

yeah.. not what you wrote

viscid thistle
#

x/a - b/a because they have the same denominator would be x - b/ a

sick steppe
#

$x-\frac{b}{a}$ is what you wrote

obsidian monolithBOT
viscid thistle
#

oh nono

#

I meant

#

(x-b)/a

sick steppe
#

then yes

viscid thistle
#

alr

#

so then what do I do next to solve the problem

sick steppe
#

$ax+b=\frac{1}{a}x-\frac{b}{a}$

obsidian monolithBOT
sick steppe
#

so clearly you need a=1/a and b=-b/a

viscid thistle
#

oh got it

#

that makes sense thank you

quick bluff
#

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

trim hemlock
#

Technically all you need is to find the spot where f(x) is undefined and f'(x)is undefined

#

Because

  1. If the function is already undefined, how cna there be a rate of change anyway?
  2. Rate of change is undefined
quick bluff
trim hemlock
#

Reasons are above

#

Not differentiable implies that the rate of change is undefined at some points

#

Or the limits dne

quick bluff
#

Isn't it not differentiable even if there's just a sharp turn?

#

That is, when the function changes?

trim hemlock
#

Yes that too

#

Usually that would be when abs sign are present

quick bluff
#

Yes

trim hemlock
#

Actually, i was wrong, scratch the first point

quick bluff
#

Okok

trim hemlock
#

Oh wait lemme see

quick bluff
#

Waler could you verify one thing for me?

trim hemlock
#

I think im confusing kyself with another fact here

quick bluff
#

The dark lines are tan x and lighter ones are cot x

trim hemlock
#

The function has to be defined first for it to be differentiable

trim hemlock
quick bluff
#

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

quick bluff
#

Am I right?

trim hemlock
#

Ermm no

#

Wait

quick bluff
#

Yeah my brain is shitting itself lmfao

trim hemlock
#

Is it the graph of |tanx -cotx| or graph of the given function

quick bluff
#

No it's the graphs of tan x and cot x

#

Imposed on one another

trim hemlock
#

Ah

quick bluff
#

The dark lines are for tan x and the lighter ones are for cot x

trim hemlock
#

Then yeah, seems good

quick bluff
#

Nono, actually...

#

Even that seems wrong kekw

#

Because there are like 6 regions where tan x and cot x switch in their magnitudes?

#

One sec

trim hemlock
#

Im not sure what you mean

#

But the graph is correct

#

The two graphs should intersect at kpi/2 + pi/4

quick bluff
quick bluff
#

In the first region, cot x > tan x

#

2nd region, tan x > cot x

#

3rd region, cot x > tan x

#

And so on

trim hemlock
#

Yep

quick bluff
#

So shouldn't it be 8 then?

trim hemlock
#

8 what?

quick bluff
#

8 points where | tan x - cot x | opens differently

#

Thereby changing the entire function

#

Giving it 8 points of non differentiability?

trim hemlock
#

Since its an oscillating function so yes

quick bluff
trim hemlock
#

That was a different problem

quick bluff
#

This discussion was entirely for part A of this question right?

trim hemlock
#

Oh wait qctually

quick bluff
#

When the mod opens with +ve, the function is cot x, when it opens with -ve, the function is tan x

quick bluff
quick bluff
# quick bluff

From here I'm able to see 8 places where the opening of the mod changes

trim hemlock
#

No no, i have mistkaen

quick bluff
#

Oh

trim hemlock
#

The sign only changes when tanx -cotx equates 0

trim hemlock
#

Lemme just draw it out

quick bluff
#

Okok

trim hemlock
#

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

quick bluff
#

Ok

trim hemlock
#

Hmm wait a min

quick bluff
#

Kk

trim hemlock
#

Im not sure how to explane this

quick bluff
#

My issue right now is by my logic the answer should be 8

#

But it's flawed somehow and I don't know where

trim hemlock
#

Ok so basically

quick bluff
#

Ye

trim hemlock
#

lets take it easy, and consider tanx - cotx

quick bluff
#

Kk

trim hemlock
quick bluff
#

Yes

trim hemlock
#

You will see that they have x ints every kpi/2 + pi/4

#

(Basically where tanx and cotx intersect)

quick bluff
#

Yes

trim hemlock
#

And is negative in portion 1, 3, 5 and 7

quick bluff
#

Yup

#

Because cot x is greater

#

And it's positive in regions 2, 4, 6 and 8 right?

trim hemlock
#

So their graph is something like

quick bluff
#

Oh

trim hemlock
#

That is what we should be having

#

Btw my sketch was wrong

quick bluff
#

This is the graph of tan x - cot x?

trim hemlock
#

Yep

quick bluff
#

Oh kk

trim hemlock
#

So now when applying the absolute value to it

#

We want to mirror the negative portion of the graph

quick bluff
#

Yes

trim hemlock
#

To the positive y axis

#

Which results in

#

Sorry not very steady hands

quick bluff
#

Yes

quick bluff
trim hemlock
#

Basically now you notice that these "sharp turns" exists at points where |f(x)|=0

quick bluff
#

Yes

trim hemlock
#

Or simply put f(x)=0

quick bluff
#

Yup

trim hemlock
#

Which there exists to be 4

quick bluff
trim hemlock
#

Huh, i just realised that, the sharp turns are always at the x-int

#

Alright thats cool

#

New knowledge obtained

quick bluff
#

Alright, now there's this one final doubt

#

when i actually graph it out

#

OHH NVM

#

NVM

#

lmao

trim hemlock
#

Yeah seems logical

quick bluff
#

the question states points where they are "continuous and undifferentiable"

#

Thanks a lot dude

trim hemlock
#

👍

unborn blade
#

is $\frac{1-\sqrt{x}+x\sqrt{x}}{x}$ the same as $\sqrt{x}$?

obsidian monolithBOT
#

Pahul's Uncle

unborn blade
#

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)

simple parcel
#

i think i know why you got $\sqrt{x}$, but the numerator simplifies as $\sqrt{x}(x-1)+1$, not $\sqrt{x}(x-1+1)$

obsidian monolithBOT
#

mchen10

unborn blade
#

my algebra skills are wack

#

can you explain a bit more

#

maybe the steps

#

i cant get it to simplify to $\sqrt{x}(x-1)+1$

obsidian monolithBOT
#

Pahul's Uncle

simple parcel
#

just the numerator

#

not the whole fraction

unborn blade
#

ohh

#

im trolling

#

ok yeah i got it now

#

that makes more sense

simple parcel
#

ok

unborn blade
#

thanks

simple parcel
#

np

unborn blade
#

Can someone point me in the right direction with this question

willow bear
unborn blade
#

obviously I wasnt

late trellis
somber sphinx
#

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

quick bluff
#

Is this correct?

rancid viper
quick bluff
#

Thank you

rancid viper
#

If you want to just derive the functions, which I think you do

quick bluff
#

Yes

#

Thought that we couldn't directly derive each function within individually for some reason

#

Thanks again hype

#

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

grand lotus
viscid thistle
#

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.

quick bluff
#

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?

grand lotus
viscid thistle
quick bluff
viscid thistle
quick bluff
#

thinkies true

#

But what does that have to do with taking f(x) as x^2 ?

quick bluff
viscid thistle
# quick bluff 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.

viscid thistle
quick bluff
#

Oh ok

#

I thought that was the end of the explanation and I missed something

#

My bad kekw

quick bluff
quick bluff
viscid thistle
#

Nope!

#

The whole function will become discontinuous as a result.

quick bluff
#

Oh yes

#

We can't use the sandwich theorem if it's just <

viscid thistle
viscid thistle
quick bluff
#

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 sully

#

Yes, it doesn't make sense because I didn't mention for which domain I'm checking the continuity for? tinktonk

viscid thistle
# quick bluff When I reread what I wrote it makes no sense <:sully:651816820122189834>

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.

quick bluff
#

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

quick bluff
#

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

viscid thistle
quick bluff
#

Oh yes

viscid thistle
#

And, since |f(X)| has two different simultaneous outputs (x^2, and -x^2), that is why it is NOT a function.

quick bluff
#

Makes sense

quick bluff
#

Thanks a lot! hype

viscid thistle
#

JEE is doable. All you need is an enthusiastic teacher (who can extend equations to real life applications) and a passion ingrained in you.

quick bluff
elfin gobletBOT
ionic vessel
#

This is dumb but how can I simplify 4^2^x

sick steppe
#

$(4^2)^x \ 4^{2^x}$

obsidian monolithBOT
ionic vessel
#

The second one sorry

sick steppe
#

it cant be as far as I'm aware

ionic vessel
#

Actually like 2^(2^(2x+1))

sick steppe
#

ok yeah, $2^{2\cdot 2^x}=2^{2^{x+1}}$

obsidian monolithBOT
ionic vessel
#

Is there anything else that can be done

sick steppe
#

not really

quick bluff
#

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

quick bluff
#

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) ?

viscid thistle
#

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

quick bluff
#

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) ?

viscid thistle
#

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.

quick bluff
#

Thanks a lot hype

viscid thistle
# quick bluff

The way you wrote f'(x) after f'(f(x)) is quite astonishing.

quick bluff
willow bear
#

is it? all they did was apply the chain rule

quick bluff
#

Or did I make a mistake of some sort?

viscid thistle
# quick bluff Wait does it look weird?

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).

quick bluff
#

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

viscid thistle
# quick bluff But isn't it differentiable around 0?

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.

quick bluff
#

Oh

#

I'll keep that in mind then

#

But is what I did incorrect then?

viscid thistle
#

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.

viscid thistle
willow bear
#

abovewater i think you're being a little pedantic here

viscid thistle
#

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.

quick bluff
quick bluff
# quick bluff

Is the reasoning correct? The question was to find K which is the set of all points where f(x) is not differentiable

viscid thistle
#

Paradon me but I am having trouble reading your handwriting. From what I can barely make, it seems correct.

dusk edge
dark gyro
#

Find the derivative of

#

is this solution correct ?

simple parcel
#

no, because youre taking the derivative with x in the exponent, so the power rule doesn't apply

dark gyro
#

ah shit wait

#

the derivative would be the same wouldnt it

#

the same as e^x/2

simple parcel
#

the derivative of e^x is e^x, but you need to use the chain rule

dark gyro
#

no not here

#

unless the book is messing with me

simple parcel
#

$\frac{d}{dx}e^{\frac{x}{2}}=\frac{1}{2}e^{\frac{x}{2}}$

obsidian monolithBOT
#

mchen10

dark gyro
#

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?

simple parcel
# dark gyro

it says that the derivative of $e^{kx}$ is $ke^{kx}$

obsidian monolithBOT
#

mchen10

dark gyro
#

but can you explain that ?

#

a bit confused how you got there

simple parcel
# dark gyro sorry had to go

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

dark gyro
#

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

simple parcel
#

i guess they just want you to use the formula first

dark gyro
#

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?

simple parcel
#

i did. the book says $\frac{d}{dx}e^{kx}= ke^{kx}$, so i just plugged in k=1/2 to get the answer

obsidian monolithBOT
#

mchen10

dark gyro
#

wdym plugged in k = 1/2

#

just randomly ?

#

or was there a reason

simple parcel
#

you wanted to find the derivative of $e^{\frac{x}{2}}$, so that's just what i did

obsidian monolithBOT
#

mchen10

dark gyro
#

omg xD

#

why did u go with 1/2 ?

#

its x/2

simple parcel
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$\frac{x}{2}=\frac{1}{2}x$

obsidian monolithBOT
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mchen10

dark gyro
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i see

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ok

molten garnet
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How do u get rid of the log thing

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Do u expand on the right or smth?

willow bear
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are these logs meant to be decimal logs or natural logs?

molten garnet
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just natural

willow bear
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natural, ok

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note that any solution to this must be greater than 21 (otherwise log(x-21) is undefined!)

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and after doing so, take e^(both sides)

molten garnet
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then I simplify and find the 2 x values

willow bear
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what you should end up with is an equation without logarithms, which you will then solve as normal

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and then, once you've got your x values, you check them against the condition x > 21

molten garnet
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ok

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thanks

hoary grail
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Because it's a perfect square?

willow bear
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yuo

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yup*

hoary grail
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ty

mild swan
hoary grail
mild swan
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How does this immediately lead to a discriminant of 0?

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How do I not see this?

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OHHHH

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Only one solution for x

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If f(x) = 0

hoary grail
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yep

quick bluff
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Not sure how I can proceed from here or if there's a simpler method

quick bluff
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The question actually asks for y'(1)

viscid thistle
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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.

quick bluff
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I should use the chain rule right?

viscid thistle
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uh yeah, but still that's not how you'd differentiate these.

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you can consider e^ln(x)=x for example.

quick bluff
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e^ln(x) . (1/x) = 1 ?

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Is this correct?

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Oh wait

viscid thistle
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so that $\overbrace{{\color{green}{x}}^{x}}^{{\color{green}{x}}=e^{\ln( {\color{green}{x}} )}}= \left(e^{\ln( {\color{green}{x}} )}\right)^x=e^{x\ln(x)}$

viscid thistle
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let me fix it.

quick bluff
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Ok

obsidian monolithBOT
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Al𝟛dium

quick bluff
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tinktonk so basically I try to convert these functions into known functions by taking ln?

viscid thistle
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kind of yeah, you are essentially manipulaying x^x so that it becomes an easier function to differentiate.

quick bluff
viscid thistle
quick bluff
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Yes

viscid thistle
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yeah you perfectly could.

quick bluff
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Nice

viscid thistle
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so that's up to you

quick bluff
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I'll give it a shot then

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Thanks a lot hype

viscid thistle
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alright, you can ping me if you get stuck.

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yw