#help-10
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I don't understand the third line
third fourth and the rest
how do we derive it for theta?
like when we take the derivative of f_x for theta what do we get?
<@&286206848099549185>
@timid silo Has your question been resolved?
@timid silo Has your question been resolved?
Cüneyt
I couldn't type it but
you got it
Ok yeh
relations are given as you see
I see
z=f(x, y) etc
One sec
I don’t understand lol
okay I understand it until the part $\pdv{f}{r}$
Cüneyt
but how do we take the derivative of "df/dr" for theta
teacher has got f_xx and stuff like that
where did they come from
I guess I better rephrase the whole question in latex
Is this partial differential
Cause I don’t know that
I cannot type it properly
but I will
just wait
Cüneyt
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i need help with this
idk how to explain this to my friend
If the oil price is 100€ and the price goes up by 20% it now cost 120€. But if it goes back down to 100€ you have only a decrease by 17%. since the difference of 20€ is less percent of 120 then of 100
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How would I solve this?
I assume I use 1-cos^2x instead of sin^2x
And then at Cos^3x-Cos^5x I'm not sure what to do
Nope, use the other one
1-sin^2(x)
That way you have a cos(x) left over that the u substitution will get rid of
Ah ok ty. Might be back with more qs on thyis topic cos I haven't fully grasped it.
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Hmm
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hey can someone help me with this please:
Let p be an integer greater than 3, show that if p and (p + 2) are prime numbers then (p + 1) is divisible by 6
11 and 13
yea i made a mistake srry its p and p + 2
ah the classic 6n-1 6n+1
if p is greater than 3 so and prime so p must be an odd number so we can write it as p = 2k + 1 and p + 2 will equal to 2k + 3
but what do i do next
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what does it mean for this expression inside the limit to “not be differentiable at 0”
To not be differentiable at 0 doesn't mean to not be defined at 0
An interval where the function is differentiable and an interval where the function is defined is very distinguishable
In fact, the function f(x)=|x| is differentiable at everywhere, except 0, so its interval of differentiability would be R*=R\{0}
But its definition set is all R
Well here, for any x different than 0, you have x/x = 1
Since the limit when x goes to a is about looking at a function infinitely close to the a value, but not exactly on it
You'll never be on 0
So by simplifying ln(x²)/ln(x²)
You're getting a constant
That doesn't vary with respect to x
So it's the limit you are searching for
that's not what they asked
u are only referring to the fraction, ignoring limit?
yeah
Definition of differentiable?
huh, why isn't it differentiable at 0 🤔
I'm not rlly with it today
I'm guessing there's a discontinuity there
Oh right, the limit doesn't exist because f(a) doesn't even exist
f(0) is undefined
f(0) gives infinity/infinity
If $800 is deposited in an account that pays 9% annual interest, compounded semiannually, find the balance after 10 years.
Need help with this
I got 1929.37122 this I’m not sure if it’s right
?
f(0) gives nothing because ln(0) is not defined
@shadow trellis Has your question been resolved?
so simply if a function’s not defined at a value, it’s derivative doesn’t exist?
because the function doesn’t exist?
why’s this not differentiable?
it's not differentiable in 0 because there are multiple tangents to that point
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How do i solve this?
I figured out that the center of the circle is (2,-1)
but radius is not known so i tried using the distance formula and got
and then powered it by 2 to get r^2 which is 40
but that looks wrong
i got radius 5
by just using completing like square
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How do I approach this problem?
No I'm going through last years exam
I start the class in a week

General form, Ax = b and it's an overdetermined system
You do $$A^{T}Ax = A^{T}b$$
dldh06
Then $x = (A^{T}A)^{-1}A^{T}b$
Is what I did so far
dldh06
So do $$A^{T}Ax = A^{T}b$$ first
dldh06
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i think we can use an augmented matrix to represent a system of equations and use gaus-jordan elimination to find the solutions
oh sorry it's been closed
It's overdetermined
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how do i draw a graph for f'
How did you number so fast?
ShareX?
its decreasing in 1, at a stop in 2 and rising in 3
ok
So what u just said
will describe how f' acts
have u heard of sign diagrams?
no
Could you try to draw a graph of f' based on what u said? try
f' represents the slope
alright, but wint it just look like the other graph
Lets start with (1)
You said 'decreasing'
That means f' is negative
So for starters, that doesn't match up
what?
I'm commenting about this
You drew that bit positive (when it should be negative)
ignore if u get it 😅
yes
Think about which part of it has negative slope
the part under the x-axis
yes
Do you also notice how the slope
is getting less and less negative
until its 0
Hope that helps you draw the graph of f' left of that point
Ok so if you have a graph of f'
The line you draw
Can only be in the bit I colored in
for the left part
Do you agree?
yes
This cannot be it. You have f' positive in bits where it should be negative
so i need to draw a graph that decreases until it hits the bottom part, and then i will star to increase
Do you see how the line I've draw corresponds to f'
its negative
Not only that
the slope gets steeper and steeper for the original function
so f' is decreasing as you towards the left
what you've drawn is correct
If you have a quadratic
ie. parabola
it turns out the line is straight
f = x^2
f' = 2x
the graph doesnt have to be a quadratic
@stray elk Has your question been resolved?
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how to transform expression in first image to second image for group theory
associativity it looks like
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does this notation mean that I should calculate the derivative while treating y as a constant and instead of x take x^2 and after all that square it?
$$ \frac{d^2f}{dx^2} = \frac{d}{dx} \left( \frac{df}{dx} \right)$$
xdk1235
Closed by @sour lantern
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how would $\frac{d^2f}{dx}$ look like?
Erzis エルジス
.reopen
✅
that's not a thing
$\frac{d^2f}{dx^2}$ is just a special way of writing a second order derivative
xdk1235
xdk1235
$$\dv{x}$$
Shuri2060
This 'thing' is an operator
that acts on functions
Consider it as one object
$$\dv{x}\dv{x} = \left(\dv{x}\right)^2 = \frac{d^2}{(dx)^2} = \frac{d^2}{dx^2}$$
This is shorthand for applying the operator twice
Shuri2060
Shuri2060
ahhh
amazing notation
really intuitive
thank you all
There are many ways to take a "second partial derivative", but some of them secretly turn out to be the same thing.
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glad I'm not alone
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i dont know why they doing that
i tried to convert 50 sec to h
and then just times the velocity by time
and then convert to meters
but its not working
d=vt, however you need to convert km to m and h to s
yeah
that's all they did
i converted to hours all units
ohh
omg
omggggg
sometimes i go blind mode
thanks for the help
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I can't figure out why this question involves the second equation which includes f(3)
That's one definition of the difference quotient
Isn't the difference quotient a forumla:
(f(x+h) - f(x))/h?
Okay give me a second to write it through
I ended up with
= (x^2 -5x+6) / (4x+4)
hang on that can be simplified right?
= ((x-5) (x-1)) / (4(x+1))
NVM not any cleaner 😦
2 things: System says it's not right and I don't understand how h = 3-x
This is the one for h going to zero. The other is x going to 3.
or x+3/(x-3)(x+1)
Isn't the Difference Quotient supposed to end with something linear?
nope
System is saying none of the answers found have been correct
now plug into difference quotient term
the (x+h) formula?
yes
Ok computing...
@halcyon creek Has your question been resolved?
its a long boi bot give me time
theres two different types of difference quotients, one of them is this and the other is simply just
∆f(x)/∆x
or
f(x)-f(a)/x-a
you get the x+h difference quotient formula by substituting h=x-a
both are equivalent
if you take the limit as h->0 and as ∆x->0, you'll see that the derivatives are equivalent too
it's just that the x+h formula is easier and more convenient for calculations at times
since everything usually cancel
s
I think I took a step out of line somewhere
very little cancelled when combining
= ((hx^2+h^2x-2hx-3h^2-3h) / (x+h-3)(x+h+1)(x-3)(x+1) ) / h
I feel like I made some computation error early in combing and have 6 variables too many
but this whole process is kind of breaking my brain as it's been years since I studied this previously
Help! I got stuck again; because inputting h = 3 - x gets me to an incorrect answer
Why are you using h at all?
because I don't know how to use the second equation given in the prompt
inputting f(x) straight gets me to (f(x) -2)/x-3
and I'm lost
Plug in the definition of f in this expression and you'll get your answer
but it didn't 😦
$$[(x+5)/(x+1) - 2] / (x-3)$$
riemann
to simplify you multiply -2 by x+1 /x+1
and end up with -2x -2+x+5
or -x+3
so (-x+3 / x +1) / x-3
but I don't know where from there because multipling by the reciprocal didn't work
a/b/c is the same as a/(bc)
so -x+3 / (x+1)(x-3)?
Do you see the cancellation
I would put extra parentheses to be careful
so -(x-3) cancels with the x-3 on the bottom
leaving -1/(x+1)?
Yes!
Thank you @tardy epoch for your time and paitence
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How would I graph f(x) = (x-3)(x^2 +x+1) ? I know that there's an x-intercept at (3,0) but how would I deal with the second part since there are no real solutions?
If youre graphing it on a real plane. An XY plane. Then the graph would intersect the X axis at only one point.
,w graph (x-3)(x^2 + x + 1)
Ohh so there'd be additional curves but they'd be below the x-axis that makes sense
Tyy!
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how did they go from 1 to 2
did they just take the common factor t
but its not working with me
yes
how is that so if i multiply step 2 by t i wouldnt get step 1
they skipped trivial steps like this
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how do we use product rule for this one
Yep that’s ur answer
When u see something like x.sinx
Use product
When u see something like x/sinx use quotient rule
When sin(x^2)
Use chain
so if we have power is chain, if we have AxB thats product and if we have fraction that quotient
Chain rule is used when ur variable in caught inside another function
For example
Sin(x^2 +1)
This is where u use chain rule
U can say x is chained inside sin

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This is the rule for complex numbers equation, can in some how tow solution for deffir k have the same answer for example
z_0=i
z_1=i
Hello is there anyone here that could help me?
<@&286206848099549185>
@karmic herald Has your question been resolved?
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struggling abit on my hw for centroids any help would be good thank you
@timid silo #❓how-to-get-help
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centroid is like center of mass from physics
$$X_c = \frac{\int dm * x}{\int dm} $$
Dev Shah
Now, did you try and graph the curves? @misty wigeon
yeah graphed the curves and added the range
Cool, so now, did you get what you need to integrate?
for an x between 0 to 1, you'll have to integral for dm first
For any x, $$ \frac{dm}{dx} = \int_{-y}^{y} (x+t)*dt $$
Dev Shah
kind of, just need to process it
I basically changed mass/area to mass/length, because we need dm to only be dependant on x for the original integration
A disclaimer though, idk any theory for centroids specifically, so there might be an easier method than this for parabolas, but this works for any function where area is defined
2/3 for top section?
okay let me know when you can if possible but i think i know how to do it now thank you for your help:)
Nw! It'll take some time to check tbh, hopefully someone else can do it before me!
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How do you simplify $-\frac{\ln{\frac{3}{4}}}{2}$ to $\ln{\frac{2}{\sqrt{3}}
ZED_118
Compile Error! Click the
reaction for more information.
(You may edit your message to recompile.)
This is it, idk why it’s not compiling but whatever
put the 1/2 back into the ln
Wait
Do you mean log((3/4)^(1/2))?
I see
Thanks
Yes
Should I close
How do you get rid of the negative sign?
put it back into the ln
Yep
$\ln{3/4^{-1/2}}$
sean
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how do you do this question
left the original number of boys, girls and adults be 5x, 8x and 2x resp.
so 5x+8x+2x=150
or x=10
so boys:girls:adults = 50:80:20
after k girls leave, the ratio is 10:9:4, so 50:80-k:20 :: 10:9:4
divide the right ratio by 5, 10:16-(0.2k):4 :: 10:9:4
16-0.2k = 9
k = 35
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We hv
Mn = 128
Mk = 64
Nk = 8
Calculate m n k
I dont have
hmm alright
divide 1st eqn by 2nd
u get n/k = 2
from this u get n =2k
sub this into 3rd eqn
u get k=2
therefore n=4
and m=32
therefore mnk will be 32x4x2 = 256
@violet radish
Tysm
np
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Erzis エルジス
you messed up a sign near the end
-(-1) is +1
i.e you should have +1 instead of -1 after evaluating the bounds
is the limit of ln part zero?
the difference of the lns with the ts, yes
it'll be clearer if you consider the difference to quotient law
yes lim at inf of $ln|\frac{1+t}{t}|$ is $0$
Erzis エルジス
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@flat anvil
I can solve a summation with i^2 in it like this
but how do I factor out the other elements in this case?
@upbeat bloom Has your question been resolved?
Was this an actual exercise? I don't see a path to computing this sum without going beyond the scope of your course.
ok then I may have done something wrong
the original exercise is this one
I think the intention is for you to just do integration using the fundamental theorem of Calculus and not evaluate that limit at all.
oh ok, thx
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How do you complete the square here?
the same way you'd complete the square in other questions
Ok
consider the part you want to complete the square for, in this case the
x^2 - 4x
and add/subtract/manipulate appropriatrly
which they actually showed in the the work
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Hello can somebody please help me
Sorry
You need to ask first
As in
Put the problem you need help with
So people who do know how to solve it can help
@old saddle Has your question been resolved?
It’s being resolved
you have three channels open
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clai
How do you draw a sketch of a graph from a derivative
do you have an example? it kinda depends
Because you can not know the y-coördinate
Does that mean that you do not draw the x-axis?
In my head it should
If you aren't given at least one value of the function at some point, you can't really graph it
But if you are
We know that a negative parabola has (a, 0) and (b,0)
a and b are given but I forgot
Oh, so you know the roots?
i.e. a parabola with a mininum
I do
This parabola is the derivative of the graph I should draw
Oh
So my question is: how do you draw the x-values without an x-axis
what is the normal way?
I guess what you can do it just draw the graph go up where the derivative is positive (the bigger the absolute value, the steeper) and go down where the derivative is negative (same thing here)
True
That's all I can say
But do I still draw the axis?
Yeah I guess
Because I can not say if the graph is negative or positive
what
yeah you can
if f(x) is decreasing, then f'(x) is negative
***most of the time
But I only know f'(x)
And need to know f(x)
given f'(x)?
Yes
well there are an infinite set of solutoins
So you know the shape of the graph
all you really need to know is the shape
Yes
cuz all of the graphs are just off by a constant
so it doesn't really matter--you don't need to draw specific values of y
yeah cuz the x's will always be the same
Because I can not say if it is above or below the formula?
wym by this
If I draw the x-axis so that the graph is negative
That could be incorrect
Because I do not know for certain that is the case
how would you draw the x-axis so the graph is negativE?
oh i c what u mean
well for ur purposes it doesn't really matter
I hope it doesn't
you can just assume that the constant would be 0
for the purpose of drawing it
and then say somewhere else that the graph could be shifted up/down any amount
if you wanted to be really specifiuc
you're welcome
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how to do
Solve by factoring
Is that 3 times -36?
then i didnt know what number multiplied to get -108 and adds to get -3
yes
you should first (to make it easier) divide everything by 3
to get:
$x^2-x-12 = 0$
Yottachad
and this is much easier to factor than the last one
Then you can do the method you were doing
yep
ok
Or quadratic formula
$(3x+a)(x+b) = 0$
Yottachad
then you would try to find a and b
mayb
Fyi factors of 108: 1, 2, 3, 4, 6, 9, 12, 18, 27, 36, 54 and 108
wait how did u get this
(1, 108), (2, 53), (3, 36), so on
That's the general form because you know if there was no leading coefficient, the form is $(x + a)(x + b) = 0$
dldh06
But there is a coefficient of 3, meaning that when you FOIL, there has to be a 3x
ok
To obtain 3x^2
so where are we so far
You just factor $x^2-x-12 = 0$
dldh06
$(x + 1) (x - 11)?$
BlzrdStrike
No
then what is it
Does -11 * 1 equal 12? And does it add up to -1?
$(x - 1) (x + 11)??$
BlzrdStrike
wait
If you FOIL, does the math check out, to make $x^2-x-12 = 0$?
dldh06
$(x - 1) (x + 12)$
BlzrdStrike
But does that sum to -1?
$(x + 1) (x - 12)$
BlzrdStrike
dldh06
idk
Did you try to expand $(x + 1) (x - 12)$?
dldh06
no
So then expand it
BlzrdStrike
Is that the same as the original problem, $x^2-x-12 = 0$
dldh06
no
So then what does that mean you should do?
hm
What are the factors of 12?
All the factors of -12
12, -1
Yes
wAYYYYYYYAYYYY
Because that adds up to -1 and multiplies to -12
BlzrdStrike
BlzrdStrike
so now ZPP
That's when you expand, but don't forget it's in the form (x + a)(x + b) = 0
what about zero product property
Where a and b where the factors you found
This isn't correct yet
Should look like this
$(x - 3) (x - 4)$
BlzrdStrike
= 0
$(x + 3) (x - 4)$
BlzrdStrike
$(x + 3) (x - 4) = 0$
dldh06
To make it more proper
yes
So zero product property, states that if given AB = 0, then either A = 0 or B = 0
$x + 3 = 0, x = -3/
x - 4 = 0, x = 4$
BlzrdStrike
You can just close each one with $
ok
$$x + 3 = 0, x = -3$$
$$x - 4 = 0, x = 4$$
dldh06
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I have a simple question about this pde. Why is there no resonance in the ansatz?
The thing I don't understand is in b, why they don't use the ansatz te^(t)(ACos(t)+BSin(t))
instead of what they do, which is just (ACos(t)+BSin(t))
cause the forcing function doesn't have e^t
cos(t) is just trig, so your guess for underdetermined coefficients is a linear combination of cos and sin
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i just need to know if my answer is correct
i did 14 x 12 x 10 x 8
is that correct^
could i get steps on how to do this question please
is it 13440?
yes
oh my bad
You count how many
are
🟥 ⚫
THEN
You count how many are
⬛ 🔴
Then you add the 2 together. For the total.
so 44?
oh
Firstly
Tell me how many are this
🟥 ⚫
Red square, Black sphere
How many ways can she result in this
14 red square and 8 black spheres
ok
Or maybe, each of these are labelled
A B C D E ...
So they are different
Now how many choices can she make?
Yes, she is choosing 1 red square and 1 black sphere
yes, 112.
Now for the other case?
⬛ 🔴
112 + 120
👌
232
Do you understand the process?
👌
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ah
uhm
Am I expected to use that to solve this question?
(solving for tensions)
Whats the Q
this
I have doubts you need it
Ah, okay
hm
I can do this when the scenario is flat
but I'm not sure how to translate that into when the situation is 3D
Find the x, y, z components of each tension, then equilibrium concept
what is an equilibrium concept(constant)?
Sum of forces equals 0
yes*
but I'm not sure how to make them so it's like
T1<cos(x), sin(x)> and T2<cos(x), sin(x)> etc.
and this is for x,y only ^
Trying to recall how to do it
okie, n
np*
@ me if u figure it out
I'll just be working on other problems for the moment
Find the unit vector of each tension
I figured out what to do
How did you get that as the unit vector?
well
Let's take T1
okay
<5, -5, 5>
so that's 5 < 1, -1, 1>
and that vector left over is the unit vector?
Not exactly what I was trying to get you to do
ahh
using i j and k?
Yes
Not exactly, that's just the distance
You understand what the unit vector does, right?
It describes the direction as a unit length
It's a mag of 1, meaning if you took some other vector and multiplied it, it doesn't scale it
Right?
Yes
So we what to find the i, j, k form of each T1
I'll walk you through the first one
Not exactly
That's the unit vector
alright
nice
So T1 time that unit vector, is what you need
Do the same process for all of the other tensions
so that calculation I did, that's correct so far then
Yes
Yep
So for T1, it's $T1\left[\frac{5 \hat{i} - 5 \hat{j} + 5 \hat{k}}{\sqrt{75}}\right]$
dldh06
yes
So that's T1 in i, j, k form
Is this what normal vectors are?
Okie
anyways, we have our Force for the first tension
and also the other 3
when we sum these, they're equal to the force of gravity (since they need to cancel each other out)?
that's..
I just expanded this
I'd prefer leaving it as $\frac{5}{\sqrt{75}}\hat{i}...$
Jukelyn
That works too
yesh
in any case, we have these unit vectors which lets us construct a representation of the forces of tension
now we would add all 4 of them and that should be equal to the force of gravity?
or rather, I guess it depends on the POV
So T1 + T2 + T3 + T4 - 150(9.81) = 0
they sum to 0, but grav is neg so it's 0+ 150 (g) = tensions
yes
wouldn't this lead to a system of 4 equations though?
Sorta
hmm
$T1\left[\frac{5}{\sqrt{75}}\hat{i} - \frac{5}{\sqrt{75}}\hat{j} + \frac{5}{\sqrt{75}}\hat{k}\right] + T2 ... - 150(9.81) k = 0$
dldh06
why the k at the end?
Because that force is in the k direction
oh right,
The weight
Now, system of equations for x, y, z directions