#help-49
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It's essentially about applying the chain rule
You have
$\int_{u(x)}^{v(x)} g(x) dx = G(v(x)) - G(u(x))$ from the Fundamental Theorem of Calculus.\
Then taking the derivative on both sides and applying the chain rule on the RHS will yield
that $$F'(x) = \frac{dv}{dx} \cdot G'(v(x)) - \frac{du}{dx} \cdot G'(u(x)) = \frac{dv}{dx} \cdot g(v(x)) - \frac{du}{dx} \cdot g(u(x))$$
Here we're assuming that g(x) is xe^x and G(x) has the property that G'(x) = g(x), i.e. it's the antiderivative.
Azyrashacorki
FTC 2
No. You don't actually have to compute the integral here.
If you did, that method, integration by parts, would be needed to compute the antiderivative of xe^x. But you don't need to do that here
you mind checking this real quick
I think am getting a better understanding
but am still fucked
sec
I think the reason this is confusing is that the choice of using the same variable inside the integral as in the bounds is making it look as the x in the bounds and the integration variable are the same. They're not.
find the area bounded between y = cosx and y = cos^2x over [0, pi]
firstly we evaluate points of intersection by setting equal to zero, I got 0 and pi/2
valid way to solve right
I have my exam tomorrow and I need to understand this really soon lol I fucked myself
could you show me how its done
for the f(x) given
x e^x
so I can see it
I'll do the weird bounds problem then I'll come back to the area one
ok
So we know that $F(x) = \int_{0}^{\sin(x^2)} t e^t dt$. Let's say that $g(t) = t e^t$. Then we could integrate that and get something like $G(t)$ such that $G'(t) = g(t)$, right?
Azyrashacorki
yea
We don't need to do it though. Since we have that, notice that with the fundamental theorem of calculus, one has that $$F(x) = \int_0^{\sin(x^2)} t e^t dt = G(\sin(x^2)) - G(0)$$.
Azyrashacorki
So then we can just differentiate to get F'(x) :
$$F'(x) = (G(sin(x^2)))' - 0 = G'(\sin(x^2)) * (sin(x^2))' - 0$$, but $G'(t) = g(t) = te^t$, so this yields $$F'(x) = \sin(x^2) e^{\sin(x^2)} \cdot 2x \cos(x^2)$$
Azyrashacorki
Why is G(0) = 0
G(0) is constant w.r.t. x, so since we're taking the derivative it vanishes.
where is the e^sin coming from
Notice that g(t) = t * e^t, so then g(sin(x^2)) = sin(x^2) * e^(sin(x^2))
Ok
I'm still confusd why G(0) is constant
isn't G'(x) = g(x)
so G(x) still has an x in it
We're taking the derivative with respect to x on both sides. G(0) doesn't have any x in it
It doens't have any t either
No it actually doesn't matter the variable in it.
We defined G(t) such that G'(t) = g(t). It's still just a function of t, so plugging in something constant will yield a constant through and through
Ok I see
can you have a look at this one
I did y^3 + 2y^2 + 1 = y^2 + 1
I got y^2(y^3+2) = 0
y = 0
y = ^3sqrt(-2)
That's fine. Now that you have the intersection, you can integrate over their difference,
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hi again, can someone help me make a tree diagram or grid table for this question βif two dice are rolled, how many possible outcomes are there having a dot sum less than 10β
consider all the choices like last time
a dice can be 1 to 6
so what numbers between 1 and 6 sum to less than 10 together
oo okay
hold on so like compatible for 6 are only 1,2,3?
sure yes
okay and so 1 can be okay with 1,2,3,4,5,6?
yes
OKAY, THANK YOU ππ you're really helpful
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idk what a "grid table" is supposed to be, but just write a table with the rows denoting the first dice's dots (from 1 to 6, so 6 rows) and the columns denoting the second dice's dots (similarily 6 columns) and just fill in all the possible combinations
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i need help with geometry
here a picture
given that AB = AC
i have to prove that the radius of the circle outscribed of ABD = to the radius of the circle outscribed of ACD
i did.
now i have to express the area of ACD using R and alpha.
i ll send the solution please tell me whats wrong
if the radii are equal of both circles why do i get different results for AC when using the sine theorem??
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idrk why is the shaded region that portion of the graph, can someone explain rq thx
The line is -1/2 - 2x which is the dotted line
yup
And then the value of y is above (>) that line's value
XD
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Find log21 9 if log3 7=a
I can't come up with a way to solve this
Looks so easy too
Please help
<@&286206848099549185>
try change of base
Like?
I should change base of second one right
i dont think it should matter
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Ok
<@&286206848099549185>
explain your question first, then wait 15 minutes if nobody has showed up man.
Ohhhh sorry sorry I'm new here
Very stuck on this question don't really understand pre algebra like that.
Oh.
Like that?
the catmullah
And when you know what z is, then you can simply plug it in the equation: 8z - 9
Ohhh.
You there?
?
@opaque timber Has your question been resolved?
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how is this true?
how does lhs = rhs
what's (*)
is that referencing something that appeared earlier?
are you sure?
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Its just long and painful
Multiply common denominator on both side.
how
By finding the smallest denominator, which is 24.
Well, if u look at the denominator for x, its 2 3 4 so, u can try multiply each side to get the 24 term
oh yeah i tried that and it resulted x=1
Left side, second expression, did you multiply 12 with all the terms in the bracket?
yes
Remembered sign changes?
Should be -5
It would be nice if u can do step by step on paper then post it here
So we can see on which steps you made the mistake
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i send it
bro
Im pretty sure u made a mistake in this step
that looks so much like a 7
nah the seven has a line
where
if i were to show u this , is this 1 or 7?
oh u write 7 like that
yes
ur mistake btw
$$- \frac{x+3}{4} = +\frac{-1(x+3)}{4}$$
whats this
JustToPro
fractions with a negative can be a bit confusing , but that -1 is being multiplied to the entire numerator
$$- \frac{x+3}{4} \neq \frac{-x+3}{4}$$
JustToPro
$$-1(6+18)$$
JustToPro
i think that's what he meant
yea
isnt the answer -1?
wait ima solve this and check
but it only results -1 to me
HOW
ok so lemme re try
for sure u getting -5 on this one
what am i doing wrong
thats a +18 not -18
ofc
yes because it changes sign
JustToPro
it changes sign if you move it in the other thing
didnt you tell me it was -18
its -18 when u wrote it wrong
when u wrote that x+3 then it was -18
but it was actually x-3 , that means its +18
howww
you said you got -5
u 2 still stuck on this?
yes
π
there are supposed to be 3 -6x
2 from the fractions which cancel out and another from the other fraction
thing is i looked at this for half an hour and said "shit theres no mistake
"
tbh im quite dumb :p
so its a mix of both thats taking this long
so what do i have to change
$$6x-6x-6x+18+4x+8+3x = 2-6x-11$$
JustToPro
JustToPro
further simplifying gives
$$7x = -35$$
$$x = -5$$
JustToPro
start
ez
Just be careful bruh
A miss is as good as a mile π
the next one looks a bit harder tho , but u can get it
it has x^2 so more terms , but it would be fine
what is blockstate btw? is it like black plasma studios that make mc animations?
they changed thier name to square media btw
No, we make Minecraft Addon for Bedrock Edition, like mods on Java
oh ok
Bruh
yes ik
It got cut out
ima guess its a 3
Assume its 0 then write "NaN" for solution π
xd
btw each question is solvable in under a sec
if u just go "multiply both sides by 0"
ez 0=0
well i gtg , gotta study some conic sections for a test π€
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For this do i need to use lagrangian to see what k actually is
Like before i do the diagram
I got k = 1/5a but not sure if thatβs right
Markscheme says that k is large so that means my answer is wrong?
where is k coming from
lol my bad k = x^2 + y^2
Not sure why my prof did that
I think to just show its a circle idk
can't you just sub in the condition and use regular derivatives
i mean, u can do it with lagrange, but u can do single var calc if u want too
makes it super easy tho
Do u mean treat as simultaneous equations?
solve ur constraint for x or y, then plug into ur objective function, then differentiate ur new objective function, and find critical points
Yeah have a feeling my prof wont want me to do that which sounds so dumb
I donβt really get the luxury of choosing methods
Now im getting a = 5/2lambda which also seems wrong
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I have a 2d pattern (for a spatial hashing algorithm), and I need to make 2 functions that would reverse an index (the numbers in the pattern) into the x (top bolded row) and the y (left bolded column). I do have a function that can generate the index from the x and the y (https://www.desmos.com/3d/9qdbtpknyt), but I can't figure out how to reverse it at all. I do have the liberty of using a programming language, so piecewise functions and such are available, but the function basically has to have O(1) time complexity (eg. it can't use iteration or anything)
@loud dawn Has your question been resolved?
if x>y: f(x,y) = x^2 + y
so i think that you can just take floor(sqrt(n))
that should be x, and y would be n-x
if y>x: then it becomes y^2+2y-x
I don't know what x and y are beforehand, so I can't see which one is greater
and would there be a more efficient way for this computation wise?
I did some research on integer square rooting, and they all had their downsides (floats lose accuracy at 2**53, other methods were all not O(1))
Precomputed table i guess
actually
I'll just round down a float I guess
x and y can only reach 2**16
and i can figure out this myself then
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ive been trying for a very long time trying to figure this one out but i just dont know how to approach it
would the power reducing identities help?
i would reckon, but those werent taught when this homework was assigned
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obviously the distance is positive but the equivalence of a & b with the remark isnt clear how we get positivity
we just show 0 iff d(x,x)
could be negative if not d(x,x)
no, d:X x X -> [0,+inf)
ik that
so it can't be negative
but then why call b positivity
because it's positivity
just say neq 0
we only know d is non negative
you are talking about a single case vs a set
and?
how is this less complex
than this
they are opposites without talking about the codomain of d
=0, !=0
ok?
Maybe it makes more sense to you but really I think we're diving into subjective territory
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How did they get from $[T(x)]{\gamma} = [T]{\gamma}^{\beta}[x]_{\beta}$ to $T(x) = Cx = Lc(x)$ for all x? Like how do they know they are equal for all x? I canβt seem to make the connection, as one of these are matrices, while another are transformations
LXDL
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how did the ^-2 become a -1?
power rule of integration
could you explain it pls?
Itβs the opposite of the power rule in differentiation
Verify this by differentiating whatβs inside the brackets
ohhhh
You should get the integrand back
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How can you tell which of these the q function is
In the textbook the method is subbing in at least one value as zero?
Iβm assuming that if itβs neither then when you sub in different values eg x1 =0, x2 = 1, x3 = 1 and then x1=1, x2=0, x3 =1, you get positive and negative answers?
Just trying to get my head around the more nuanced examples :/
Is the q function positive definite?
<@&286206848099549185>
I'm not sure what the definitions are for you but the way I learnt this was to write it as a 3x3 matrix $A$, and check that the determinants of three principal minors $A^{(1)}, A^{(2)}$ and $A^{(3)} = A$ are all positive, then the matrix is positive definite. Principal minors are the upper left 1x1, 2x2 and 3x3 matrices of $A$
lgkoo
Yeah thatβs a good method, whatβs really strange is though is that our prof told us to skip that section
But is still asking these questions on past papers bruh
Is there any other way?
not that I can recall soz
I just found this from my profs notes
In your opinion would u even say this is valid
Icl this is a joke that he made us skip the solid method
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Hm I have a matrix
0 -1 -1
0 2 0
1 4 -1
and determined its characteristic polynomial xΒ³-xΒ²-x-2
Its elements are from a set F3 btw, but I consider it isomorphic to Z/3Z
The eigenvalues I found are 1 & 2 but I'm not certain whether they are correct
Since for 1 I get an empty eigenspace
@unique stream Has your question been resolved?
If its over F_3 the you canβt have negatives
The only numbers available are {0,1,2}
Hm why would that be
[-1] would be in the equivalence class of [2] for instance
Thats exactly right
So you have to begin by transforming the matrix into its equivalent form over F_3
yh but I still receive 1 & 2
Can you show your working
shouldn't change under equivalence properties
sure a sec, different setup
For the matrix we'd have
0 2 2
0 2 0
1 1 2
and the characteristic polynomial is
x * (x-2) * (x-2) - 2 * (x-2)
inserting 1:
1 * (-1) * (-1) - 2 * (-1)
= 1 + 2 = 0
making 1 a valid eigenvalue @odd solar :/
how did you get the eigenspace ?
@unique stream Has your question been resolved?
Well Av = 1v
Which gives me only a set containing the zero vector
Can confirm, using Sage
Hm yeah but isn't it odd that 1 would be a valid eigenvalue then
ofc lol
I was wondering about how you solved the system
maybe there's some reduction mod 3 you didn't notice somewhere
actually
A - I is
[-1 -1 -1]
[ 0 1 0]
[ 1 4 -2]
if you reduce the last row mod 3, you get [1 1 1]
so row 3 = - row 1
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Range of sin^-1(x)+cos^-1(x)+tan^-1(x)
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anyone can help with chemistry balancing redox equations
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]
the area needs to be in teh form of aln(2) + b
however after integrating this between the points ln 3 and ln 6 (which are the points at which the graphs intercept), the area isn't coming in that form
$$[A = \int_{\ln(3)}^{\ln(6)} |(18e^{-x} - 6) - (3 - e^x)| dx]$$
Emploice Muswashans
this woudl evaluate to
$$[A = \int_{\ln(3)}^{\ln(6)} |18e^{-x} - 9 + e^x| dx]$$
Emploice Muswashans
Take an integral?
hmm yeah I did that
But I didn't quite get the answer
in that format
oh wait nvm I think I got it
sorry I think my brain was just being dumb
Thank you so much
sorry to trouble ya
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This is coulombs law i got this problem how should i solve it without prefixes
Should i input it without prefix im not really sure can somebody help me out this problem
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how do i do this?
try multiplying out the right hand side and then comparing coefficients to the left hand side
i dont get what to do
i dont get what you mean
yes
alright
now do the same thing for the right hand side of the equation, (x-1)(x+a)(x-b)
how do i do it in this case
i havent done it with 3
start with the first two
(x-1)(x+a)
then once you get that result, multiply the result you just got like -> (...)(x-b)
it's the same procedure but you do it an extra time
@vocal steeple Has your question been resolved?
What did u get
x^3+ax^2-x^2-ax-bx^2-abx+bx
Seems correct now solving for coeffs should give the value of a and b
and how do i do thyat
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I need help with question 1(ii) i am not too sure how to get the Phase current Ica
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<@&286206848099549185>
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Hi i need help for this <@&286206848099549185>
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Hey how do i paratetmerize #3?
I got something like
r(x,y) = <x, y, 3x-2>
then i got something like this for my integral
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@burnt prairie Has your question been resolved?
I believe you want to parameterize wrt r and theta
so the param should look like
[ \sigma (r, \theta) = (r\cos\theta, r\sin\theta, 3r\cos\theta -2 ) ]
shsgd
in this case what is r
radius
no, it would be the radius of the cylinder
yes, but pre-emptively subbing in r=2 will lead to different result
not sure to be honest, but I computed it both ways and got a slightly different result
12sqrt10 pi and 20sqrt10 pi
ah
im guessing the 2nd way is pre-emptively subbing in
cuz thats what i kinda did
yeah
12pirt(10) is correct
I guess its because in the parameterization, the z component is a function of r
hmm
but i'm not certain
or maybe if we lock r we are only saying its a circular projection?
actually that doesnt make too much sense
anyway
alr for the future ill try to rememeber that
im guessing its also because if we lock r we only have 1 variable
and that shouldnt give a surface
well the only difference in the calculation I got was from the
$\abs{\sigma_r \cross \sigma_{\theta}}$
shsgd
ah
root 10 vs r*root10
how do you even caluclate a cross product if you only have theta
[ \sigma (r, \theta) = (r\cos\theta, r\sin\theta, 3r\cos\theta -2 ) ]
shsgd
or do you mean when subbing in r=2
ohh
since its a change of coordinates you would need to account for the Jacobian
which is rdrdtheta
yes
alr ty
I'd just stick to not subbing in just in case
ye
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how do i approach this problem, i tried seperating them into 3 surface and used stokes but got 0 as the answer for all of them. the answer should be 104pi/3
Image
am i suppose to use stokes in this case or just evaluate the flux
Please don't occupy multiple help channels.
Evaluating the integral over 3 separate surfaces and summing should get you your answer
like
using stokes theorem or no?
or just literally do the siurface integral
@odd solar
Either way should result in the same andwer
whattt
im so confused
i got 0
so for the cylinder
i did parameterization of (theta, z) = 2cos(theta), 2sin(theta), z
i then find the nromal vector by
and then change the vector field with the parameterization
then dot product and evaluate the double integra;
is this how it goes?
I believe your parametrisation is wrong
why
Using cylindrical coordinates
Ah no sorry, iβm tripping
The parametrization is correct
Then you need to evaluate
[ \int_{\sigma} \mathbb{F}(\sigma (r,\theta) \cdot \abs{\sigma_r \cross \sigma_{\theta}} rdrd\theta ]
shsgd
this is what I did
Hang on let me get some paper
ok
i tried to compute the line integral of hemisphere with the boundary using stokes theoreom, i got 0
for that
for the disk i tried to get the curl and dot it with the nomnrla vector with parameteization (r, theta) = (rcos(theta), rsin(theta), 0)
also gave 0
oh btw the answer should be 104pi/3
once i try to solve by getting a curl and dot with nromal vector, all teh answer are 0, which is so confusing
oh btw i think its helpful to mention this problem is under the gauss theorem section
hmmmm
And you say the surface integral over F of the cylinder should be 104pi/3?
oh btw
for the hemisphere
is the parameterization of (theta, phi) = (2cos(theta)sin(phi), 2sin(theta)sin(phi), 2cos(phi) + 3)
correct?
For what bounds of theta and phi
Yeah I believe that should be correct
okay
Have you calculated the integral over the hemisphere yet?
not yet im doing rn
the normal vector is tough to calculate
its so long
is it supposed to be this long
Yeah
Stokes theorem would be better for hemisphere
In retrospect
Sorry its very late so my brain isnt 100%
Stokes should give a line integral
Yeah
Iβm falling asleep and my brain is not working, iβll write up a solution in the morning if no else gets to it
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do i solve the second problem the same w ay as i solve the first problem even though the first is a power and the second is a maclaurin?
a maclaurin series is a particular type of power series
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@serene skiff Has your question been resolved?
@sharp coral iz this right so far? Is y prime of 0 negative 2
seems right so far
i got that the first four terms are 1 -2x + x^2 -(x^3)/3 does that seem right
actually wait aren't the equilibrium points just (0,0) and (-1, 0) then?
<@&286206848099549185>
Can u help me my homework? @sharp coral #help-42
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<@&286206848099549185> can anyone help pls?
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Hint, what is $x^2$
Xwtek
No, I mean express x^2 in terms of p
Just plug in x = ... into x^2
Yup
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how to differentiate it with respect to (B-V}
differentiation happens with respect to a variable
you should give more context for what you're doing
b-v is the variable
so this is for error propagation of astrophysics
i need to find the standard deviation
of T
where
do B and V have some kind of error bounds?
Usually what people do in physics is they approximate
$$|\Delta T|=\left|\frac{\partial T}{\partial B}\Delta B+\frac{\partial T}{\partial V}\Delta V\right|\le \left|\frac{\partial T}{\partial B}\Delta B\right | + \left | \frac{\partial T}{\partial V}\Delta V\right|$$
where the inequality is the triangle inequality
which should not be confused with "the standard deviation"
because the standard deviation relates to random variables
oh sorry i didnt explicitly mean standard deviation
by standard deviation i meant the error range of T
umm theres been another mistake too
sorry
B-V
Stipendi
So B-V is thought of as a single variable that has some error bound?
yeah
well you should probably call it something else
its called colour excess
In that case you don't even need the triangle inequality
if you wish to do a linear approximation
yeah i was wondering that this shouldnt be that hard
the triangle inequality isn't hard
So I suppose your question is how you differentiate the function 1/(x + 1)
1/(ax+b) = (ax+b)^(-1)
and thus the derivative is -a(ax+b)^(-2)
@old citrus Has your question been resolved?
so for the derivative of the whole thing
i just keep 4600 on the outside of brackets
and inside
i keep sum of two fractions
of -a(ax+b)^(-2)
?
sorry for replying late
my electricity went out
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e
i cant help but notice
I mean i cant help but question
Where did the formula
if f(x) = ax + b / cx + d
Then f^-1(x) = -dx +b / cx -a
Came from?
so x(cy+d) = (ay + b)?
yes
yes
(cxy + dx - b)/a = y
how do i remove the why on the left
oooohhhh
That make sense
also one more thing
What is it called again when the power is on the left of the number
so its like
$^3 x$ ?
artemetra
yeah that one
tetration
you are talking about $x^{x^x}$ right
artemetra
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solved everything until question D
I just don't get the coordinates of the stationary point when I revert back
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I worked out a and b, and I just realized I was wrong with part b but idk why
Sending the work rn
Ok I think itβs because I solved for c after I already had an equation which is wrong
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Yea ok I figured it out
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Hey guys, I need help with a calculation:
A vector, πβ
, is given below
πβ =(β15 over β8)
What is the length of πβ?
In this picture, I followed the hint for calculating the length of this vector, but as I calculated it I got so confused because, I started with calculating -15^2, but every calculator I used said it was -225, I don't understand why?
The Ψ―
yes
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Do you know what an area scale factor is? If you don't try to find out and then try tyhe problem again
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Help
I donβt have any questions in particular
just post those and you gonna find out
it will take faster for sure instead of saying
Iβm not necessarily looking for a right answer but Iβm curious if you spot anything that may look wrong
Itβs mainly the first page Iβm worried about
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Hii
How do i find sin and cos
3 = 3cos(theta) 
Is that part right? π
Well you need to solve
I pur in 3sin(theta) in for x
Niklaus
More that you can find cos(theta) very easy from here-
Oh wait 3 = 3 - sin π
Niklaus
she's already done the simplification so just needs to consider this
Idk why i put cos π
Oh? 
after getting this, or?
Niklaus
OH I KNOW WHY I PUT COS
You cant separate the 9 from sin theta like that
3 - COS
You end up eith
So, if you know that 3cos(theta) = 3, then cos(theta) = ?
What if u factor it
Niklaus
No but sin is squared
So u use the trig property to turn it to cos^2
(and we've said @coral bobcat has done the first part already...)
1-sin^2
I thought they wanted to verify. That part
Sorry
Long story short
Yes
Ur that part is good
1=
You know cos(theta) = 1, and you can relate cos(theta) to sin(theta) easily 
You can? π
Yes, you can, and you already have in multiple places! 

OH
So if i put it back in the sqrt
Then sqrt(9-(3sin)^2)
And then
Sqrt(9-(1-sin^2))
Oh
π
Solve for theta my friend
(easier to e.g. notice that you know the sin^2(theta) + cos^2(theta) = 1, and that you deduced cos(theta) = 1, so...)
That too
Niklaus
Why did you change it 
Huh?
Said it was correct originally 
No
When it was sin?

