#help-0
1 messages Β· Page 282 of 1
yeah, pretty much
yup
and that as he only answer?
not x = 6
cause x = 6 is y = 4
and its not asking for y = 4
its asking for y = 2
the only input which ouputs 2 as far as I can see is x=4
yeah
π
.close thanks I was understanding till the part about the "= 2"
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How can I find the value of alpha?
I got a partial work, in order to complete it I need to find BD/CK but idk how, or maybe there is much simpler way
i would say the sin rule if you know it
Where specifically?
actually i dont think its even necessaru
since the triangle is isosceles
the one with side length 8
Did you notice this triangle? You can work out alpha from there
I don't see how can it help
wait what im stupid
How? Notice that the 82 degree angle is ABE, not ABC
Since the sum of angles is 180
you know 2 angles in the triangle
I don't
There is 82 and 90 (the right angle)
At the picture
the 82 degree
Is
ABD
NOT
ABC
The angle inside the triangle is 82 minus something
oh my mistake
Do you mean ABD = 82 deg ?
Yes
my bad
Maybe it wasn't clear as I thought
ok once again i suggest the sin rule
Good recommendation
with the entire triangle
What triangle
Which
He/ she/ it meant ABE
You could just use "they"
oh yeah i forgot i set that
I'm not into the "pronouns" thing
So if I use the sine rule
honestly speedran the enter to the server
It's not about pronouns, if you don't know someones gender you can call them as "they" and it will be grammatically valid
That's just how English works
sorry i'll actually set them, i thought they were mandatory so i just picked at random
Yea I can find angle BEA
And then the other angle
I can't believe I didn't see that
I am so stupid
And when you find AEB , what do you do? (just to see if you need further assistance)
Azu?
Yup
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3^x=2
2^[(x-1)/x]=?
,rotate
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3. I got an answer but I'm told it's wrong
4. I got an answer and would like my work checked
5. I have a question about someone else's worked solution
6. None of the above
2
what have you tried?
you are
can you show the steps
sub the value of x
!nosols
As a helper, please do not give out answers that could be copied as a homework solution. Have the student work through the problem themselves and guide them along the way.
did that then?
show me
bad writing but
no worries
2 is the base
why is 2 in the air
you got x as?
log3(2)
now use loga-logb = log(a/b)
hmm
now again use base change property
so write it as a-b?
nah
what is base change proprty
whats logc(a)/logc(b)
oh
use this
so its logb(a)
yes
2/3
how
.
.
oh lol thanks
3/2 or 2/3?
its supposed to be 3/2
im confused a lil bit
i think its 3/2
it is 2/3
is the right answer i made the mistakes
no i wrote it wrongly
how how
look up
try to solve it again, with a nice pencil
yeah thanks for the help i need to write better
.close
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simplify it to 30 * -3f * -7g
?
f(-3) means the value of the function f at the point x=-3
So you can replace f(-3) with -3
and if g(-7) then 7
oh
oops
sso
-6(-3) @worn fox
and 5(7)
if replacing them
What is g(-7)?
its y = 7
look
Are you sure
Again^
uh
Youre conjuring a multiplication out of thin air :p
are we just forgetting about 5g(-7)?
You have $(-6f(-3)) - (5g(-7))$
Ξ£ΞC
Precisely this
this is all we are doing?
but then why would we need the entire graph
To find the values of f(-3) and g(-7)
we did tha
and it came out as y = -3 and y = 6
so where do we put the -3 and the 6
Right so you plug those into here
into the f and g??
You have found that f(-3) = -3 and g(-7) = 6
yes
So that is what you replace in here
so
(-6(-3)(-3))-(5(6)(-7))
that doesnt make sense
we ae replacing f with -3
and g with 6?
is what your saying
You replace f(-3) with -3
f(-3) is not f times (-3)
It's the value of f at the point x=-3
so (-6(-3)) - (5(6))
Yes
i thought thats what i said though
replace the f(-3) with -3
and replace g(-7) with 6
Yes but then you multiplied instead of taking away and then asked why we needed the whole graph
-12 is correct
oh
why did we take it away though
how do I see next time that I'm suppose to take it away instead of doing other things with it
Because this is what the question says
They are using a dot when there is multiplication
i thought that was negative 5 
it was but I didn't know
I was suppose to combine
5 with g
You thought it was $(-6\cdot f(-3))\cdot (-5\cdot g(-7))$
Ξ£ΞC
yeah
But see i had to add brackets and another mult symbol to make it that
i see
so thats wht you meant by "summoning an equation out of nothing"
Right you added a multiplication that didn't exist
Remember your orders of operations too
Do the multiplications first and then addition or subtraction
yeah I know that but I just got confused with the -5 lol
It's okay now hopefully you won't be
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How to integrate this by substitution the eight part is what i am not getting
Should i do 8u
what have you tried
Sending bpictrue
there is to be an 8x
it looks correct, now just come back to the original variable x
but i need the 8x
why 8x
answer might be different due to constant
according to this
8(x-2) = 8x - 16
we can "remove" -16 (derivative of a constant = 0)
so it becomes 8x
im integrating
Why derivative
int of 2x = x^2 + C, yes?
we can say answer is x^2 + 1, x^2 + 2, x^2 + 3, x^2 - 1000 etc.
and we're still right
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I remember how to solve this but I dont really understand the logic
I just replace a with y'(t), b with x'(t) and replace x with x(t) and y with y(t)
I dont really remember why I replace a with y'(t) or b with x'(t)
dy/dx = dy/dt * 1/ (dx/dt)
What does this come from sry
derivative rules
we already went over this something like 2 or 3 weeks ago I think
if y = ax+b, then you can rewrite this as y - ax = b
so it's enough to find the slope
oh wait
in this case
nice little linalg trick
oh well you already know
but there's a similar proof to the one for the normal vector and the plane equation
because it's basically the same thing
I don't think OP is there yet. Maybe keep it simple.
Ye im dumb π
Lol. No. Not that.
because if a line has directing vector (a, b) then (-b, a) (90Β° rotation) is orthogonal to the line.
So all vectors of the line are described as being orthogonal to (-b, a), which means (-b, a) . (x, y) = 0, i.e. -bx + ay = 0
which gives back y = b/a x, with b/a = dy/dx
so you can take b = y'(t), a = x'(t)
(and it turns out there's a very similar proof to why a plane with normal vector (a, b, c) can be described by ax+by+cz = d)
But what has this got to do with orthogonal lines sry
just using the dot product as a way of describing lines
like you can say "the x-axis is the line of all points orthogonal to (0, 1)"
every line, as such, has a set of orthogonal vectors
OHHHH WAIT
if (a, b) is a directing vector, then every point is of the form L(t) = (at + a0, bt + b0)
Then (-b, a) . L(t) = -bat -ba0 + bat + ab0 = ba0 + ab0 is constant
I just got it
So all vectors of the line are described as being orthogonal to (-b, a), which means (-b, a) . (x, y) = 0, i.e. -bx + ay = 0
This makes sense
that one is a result you'd only really see when studying linalg an euclidian spaces
I had to reread all your messages like 10 times hahahaha but I finally got it
because then you prove it for any dimension
so it's fair that it's hard to understand for you
Hopefully I never have to do that π
depends on how much math you come to do
This is hard enough hahaha
but don't worry, you'll be a lot more mature when you get there
math is about understanding and visualizing sometimes
I am just a square brain
Yeye makes so much more sense now
high school is crunching numbers, undergrad is having intuition to carry you
I miss when all I had to do was crunching numbers π
the great students are the ones that manage to get that intuition in high school
True tbh
and there aren't exactly many
at least not in your standard school with your standard teacher
where the objective is just to know the few techniques needed to pass the exam
(this is not india btw)
I dont need to just pass my exam I need 70% minimum to get accepted π
US ?
I forgor
that's "passing" if you define it conveniently
I guess haha
who cares if the bar for success is 50% or 70%, it's a bar
Yeye true, a high bar tho lol
didn't say it was easy
And its a hard test (for me anyway)
if you got an translated version I might enjoy taking a look at it
unless it's transparent enough
I actually do 1 moment
I think youre on my friends list so I will just dm it
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I have a question about about a Fourier Transform
well nobody will be able to answer the question if you don't ask it
Technology being difficult one sec
I am stuck at the end part here
The provided answer looks like this
And I have gotten it to here
Did I go wrong somewhere or are these actually equal
@lean wraith Has your question been resolved?
.close
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I need help with this question
was thinking of deriving the cosine using triangles and the pythagorean theorem but i don't know
@violet bear Has your question been resolved?
@violet bear Has your question been resolved?
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ok, given $B^TB=n, B, X \in \mathbb{R}^n\$
show $\frac{1}{n}||X-\frac{1}{n}(B\cdot X)B||^2=\frac{1}{n}||X||^2-\left(\frac{1}{n}(B\cdot X)\right)^2$
you should probably have an equals sign or something
Frosst
do you just open up the parentheses with dot product
now if we ignore the 1/n and expand the norm on the left $\left(X^T-\frac{1}{n}(B\cdot X)B^T\right)\left(X-\frac{1}{n}(B\cdot X)B\right)$
Frosst
that gives $X^TX - \frac{1}{n}(B\cdot X)X^TB - \frac{1}{n}(B\cdot X)B^TX + \frac{1}{n^2}(B\cdot X)^2B^TB$
Frosst
now since both X and B are R^n vectors, X^TB is X β’ B and B^TX is B β’ X and we know those are the same
$||X||^2 - \frac{2}{n}(B\cdot X)^2 + \frac{1}{n^2}(B\cdot X)^2 B^TB$
Frosst
then we use the identity of B^TB = n to simplify it to
$||X||^2 - \frac{1}{n}(B\cdot X)^2$
Frosst
i get the 1/n i left in this step
$\frac{1}{n}\left(||X||^2 - \frac{1}{n}(B\cdot X)^2\right)$
Frosst
ok i just needed to use latex to figure this out i think this is right
@mellow grail if u wanted to see
(except i need to go the other direction but that should be trivial)
ok thank you for the help channel and latex bot
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IM trying to solve this question.
Do you know what's slope of a tangent?
I know you can obtain the equation of a tan line by using Y - y1 = m(x-x1) when given a value, thats what I was doing up until now. But this is a bit different which is why I thought to ask. My work here is based off the tutorial the webassign gave me... Unfortunatley its not very helpful though.
OH, wait.
NVM. i was just writing my answer wrong.
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Be more specific
ok
so for example, n=1 is the first term
a_n is the number of quilts
quilt squares
There's a more explicit pattern emerging i think
Take a look at n = 3 in particular
ok
What does 5 mean in that photo
Number of blue squares for sure
yup
If i had to describe it in words
n is the term number, while a_n is the number of blue squares in the quilt
How to tell if a square would be blue or not is tougher to describe
I definitely think so too but i really am not sure what pattern the blue squares follow
I mean, the upper-rightmost and the lower-leftmost square are always blue so you can set either one as a baseline and say the rest follows a checkerboard pattern
yeah, we could also say that
what if the pattern is
the n term value divided by the total squares
for example
4 (the total squares in the quilt) divided by 2 (the term number)
4/2
which gets you 2
Well that fails with n=3
I think you have to state what n represents in terms of the quilt
We already have a_n as the number of blue squares in the design
yup
But we may have to be more specific than stating n as the index number
Well, in n=2, are there 2 squares in the quilt?
nope
maybe the n value represents the side of the quilt
for n=2, their are two squares at the side of the quilt
and for n=3 there are 3 squares at the side of the quilt
Yep, this works!
yay
You theoretically can just bash it
oh
alr i shall do that
so i got a_n = 13
for n=5
im trying to figure out a pattern
Yeah sounds right
Yeah, what part of the question do you need help for now
Yeah just plug in n
yup
@upbeat gorge alr i gotta go, this looks pretty simple enough so i think i can finish this on my own
thanks for your help!
Ok, no problem 
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for b is it just 3000(1+0.005)^2
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AD is parallel to BC not not equivalent?
at least i think thatβs what the arrows mean
fuck
geometry exam tomorrow lol, iβm doing last minute studying
i donβt think that that necessarily proves it but i just want someone to check me
It does prove it since AD = BC as well
explain?
Construct AC
?
Draw AC
ok?
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differential geometry -
Is there some metric space where all geodesics (in any direction) converge to a point, or at least converge together? 
I'm thinking of a black hole and how "all paths lead to the singularity" but I don't think that's an accurate statement
this started because someone said all roads lead to rome and my mind got a little distracted
I don't suppose spherical counts
I would also settle for all geodesics getting arbitrarily close to a target point an infinite number of times
yeah I want all of them
something involving projective geometry and infinity maybe?
one basic issue here is that going "backwards" on a geodesic would, in theory, take you away from whatever point
double sided Gabriel's horn seems neat but has some issues
i am very much enjoying following along on this conversation
I'm imagining starting with a euclidean disc and using a metric where distances are larger the further from the center you are
I feel like that would have a tendency to suck in geodesics towards the center but I don't really know how any of this stuff works
I think you could easily construct orbits or something on that, and if you go directly away from center you're not coming back
but that's a good start! this problem seems fun
One note with orbits is that there's no inherent notion of velocity
So I don't know that a periapsis and an apoapsis should really behave differently
And it feels like a circular orbit is only stable for a very specific metric
or well, perhaps there's a lot of metrics where a circular orbit is stable for one specific r but it feels like by making the metric extreme enough we can fix that
Maybe we could base it on elliptical geometry instead of euclidean to get rid of the problem of a line leading directly away from the hole
Or well, just spherical
Is it allowed to start with a Euclidean disc and identify antipodal boundary points with each other
@tardy stag Has your question been resolved?
i guess if we start with the euclidean disk and tie all the edges together it technically works but that absolutely feels like cheating so hmm
okay if we just want a space where every geodesic crosses over a certain point we have that it's called a circle
ugh i don't feel like i'm qualified to answer this question anymore
@tardy stag Has your question been resolved?
not going to leave this open for too long because it's both specific and ill-defined and i really need to re-learn differential geometry before i can get an answer to it, but essentially:
I'm looking for a metric space such that all geodesics, starting at any location except perhaps the point P, have the same limit of P
this may be impossible
just a suggestion, but maybe the folks at MathStackExchange or MathOverflow can help you with your question
yeah that's probably the next step
that, or actually figuring out what i'm asking lol
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Approximate $\sqrt{\pi}$ using the local linearization of $f(x)=\sqrt{x}$ at the point where $x=3$.
Jash
!status
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6. None of the above
hmm whered you get stuck?
this means to assume that, near to some point, the function is just a line
oh
mechanically it means constructing the tangent line
so i find the tangent line of f at x=pi?
not quite
x=3
yea, construct the linearization at x=3
then you just assume that for values near 3, like say pi, the approximation will be OK
so like f(3)=sqrt(3) and f'(3)=1/(2sqrt(3))
so y=(1/(2sqrt(3))) (x-3)+sqrt(3)
so do i just plug in pi?
yea, into your line
can i just use this to approximate any value of f
No, not any
well it doesnt make sense for every value
the domains dont match up
but otherwise yea, the approximation just gets poorer and poorer
its pretty good here
oh ok
uh so the next part is Determine if your approximation is an underestimate or overestimate of the actual value of sqrt(pi). Justify your answer.
there are a few ways you could go about this, whats your thought
can i use a calculater to just like compare this value to the actual value
how would i do it otherwise
you have a few ways
one would be to take a number ||a little smaller than your estimate, square it, and show that this squared is still xyz||
alternatively, you can look at derivatives
you know your approximation is equal to the function at x=3
my teacher was talking about like using the concavity of the function
whats happening from there
yea
you can show that sqrt is pulling away from this line
,w second derivative sqrt(x)
clearly the second derivative of the line is 0
ye
would i evaluate at pi or 3?
just make an argument for an x in the area
i mean ik it doesnt matter in this case
the rate of change of our line isnt changing
but for the sqrt line, its decreasing
that seems sufficient to me
is anybody watching
oh so like the line is always increasing at a constant rate but the sqrt graph increases at a decreasing rate
implying that the line is above the sqrt near x=3
sqrt increases less than your line
because its derivative will have decreased when you moved rightwards of x=3
this is always negative if its not clear that part of the argument
can you argue it?
since S is concave down, the approximation will be an overestimate
that seems fair to me
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how to do this?
you have 101 numbers, one of them is 10,000,000 and the rest are 2, their average is?
@simple saddle Has your question been resolved?
but how can i do without calculator?
do you know how to divide numbers without a calculator?
long division, etc?
you have here an eight digit long number but dividing by 101 is not even that much time consuming or painful.
ya but won't it be still time consuming
can we estimate using the data
well maybe if you have 5 seconds to solve this question
then yeah it will be time consuming
are you at least able to write down the exact value of the average as a fraction Y/N
yeah
10,000,200/ 101
ok great
do you know how to do long division
i promise you this is not any harder than any other long division problem
okk
trying to do some big brain estimation gymnastics will be harder
okay ann
thanks
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'
Where will the friction force go ?
please don't close and reopen a new channel just to ask the same question
ok sry
is the applied force just 8N?
what is going on in this photo
yes
then my intuition says friction force points up
and also the weight
but how
is the box at rest?
it's about to move
??
sry I edited
i mean it doesn't matter tbh
friction points up here I'm 95% sure
the gravitational force exerts 10N on the block downwards
while the applied force exerts only 8sin30 N on the block upwards
so friction should point up
to help the applied force counter gravity
You're right but how? doesn't friciton work in the opposite direction of the estimated direction of motion?
what do you mean?
friction opposes movement
yes
so then, what's the issue?
when the object moves it will move upwards right?
how would it move upwards?
the force F points in that way
yeah but you can't ignore gravity
who is stronger than the y component of the applied force here
so w/o friction, the expected result is that the block falls
the 10N is Fg, yes?
aha now I get it
or am i wrong
What's Fg
gravitational force
yup
π
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hello every1
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Hi could someone help me with this problem
We have to find the percentage of shaded area for the shape
It seems basic ik, but I have no clue what to do without assuming anything
Are you familiar with the formula for the radius of the circle inscribed in a right triangle?
Wrong channel
No i'm not
never heard of it
It's equal to (a + b - c)/2 where a and b are the legs and c is the hypotenuse of the right triangle
Want to see how this formula is proven?
Yeah that would be great
Okay, let me draw a diagram
Wait so we simply have to substitute a value for the legs, calculate the hypotenuse and then divide by two to get the radius
alright thanks
Yep
Let's call the horizontal leg a and vertical leg b for convenience
Alright
oh yh thats true
So we have IH = a - r and EF = b - r
yep
Now, thanks to the symmetry, we can say that FJ = FE and HI = HJ
But FJ and HJ add up to the hypotenuse, c
wait so we can just assume that
So c = FJ + HJ = FE + HI = a - r + b - r
The symmetry can be proven, you would just need to show that the right triangles are the same
oh alright
So here you isolate r and get r = (a + b - c)/2
alright yeah i follow
E.g. the right triangles JDH and DIH have the same hypotenuse and legs (DJ and DI) are equal, meaning the other legs (HI and HJ) are also equal
Similar argument for the other ones
Okay, so, using Pythagorean theorem, you can show that the hypotenuse here is x * sqrt(2)
And simply apply the formula
That's it
alright wait
so (1+1+sqrt(2))/2 = r
then r^2 x pi equals the area
and then u just divide that by 1/2 to get the percentage
Yeah, x shouldn't have disappeared though
what do u mean by that
Should be $r = \frac{x + x - x\sqrt{2}}2$
A Lonely Bean
Oh and the minus sign too yeah
oh ok mb
yh i screwed that up
but you can still substitute 1 right
or any number and u would get the right answer
Not really, you can't assume the answer is a constant no matter the value of x yet
Unless you realize that when you divide, the x^2 terms cancel out
Then sure
Anyway, this means that $r = x\frac{2 - \sqrt2}2$ and $\pi r^2 = x^2 \frac{3 - 2\sqrt{2}}2$
A Lonely Bean
alright so ((2x - x * sqrt(2)/2)^2 x pi) / 0.5 would get me the percentage
Oh I forgot about pi here my bad
Yeah
dam
thank u so much
i've been stuck on that for half and hour
ur actually a life saver
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I didn't get the bottom right part
it's a sleight of hand
yeah, exactly. they're doing black magic.
i mean here you can substitute t := 2^(1/x) and acknowledge t -> +β
then you have (t-1)/(t+1) = (1 - 1/t)/(1 + 1/t) -> 1
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how do i draw y^2=x^2-1
yes , how is this a hyperbola thouhg
it's a hyperbola aligned differently wrt the axes
x^2-y^2=1 is easier to understand
is it the same as y=+-sqrt(x^2-1)
by graphing both of those
no it is not
lmao
oh wait it is
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how tf am i supposed to makje this a fraction
By doing it without a graphing calculator? Consider integrating
What exactly is the teacher asking for? The same as what's asked for here?
Well some of the coefficients will be fractions
something like this
with 0,2 being a postivive integral subtracted from 2,3
positive
Yeah for part d you don't need to have bounds of integrations, just integrate indefinitely and choose the value of +C correctly so that s(0) = 1
i did d already
just c mb
but my brain hurts trying to turn that into a fraction
like how
i only need to integrate 0, .55 - .55,5 right?
This is really weird, they give v(t) only at the end?
Anyway, to get the distance travelled you need to integrate the absolute value of v(t) rather than v(t) itself
So $\int_0^5(2t^2 - 12t + 6)\dd{t} = \frac{2\cdot5^3}3 - 6\cdot5^2 + 6\cdot5$
Wait no
A Lonely Bean
The antiderivative is 2t^3/3 - 6t^2 + 6t and when you plug in t = 0, it's 0, so just plug in t = 5
So this is just 250/3 - 120, can you make the denominators common here?
Damn I made the very mistake I warned you from doing lol
Yeah but that's gonna be irrelevant as we have to integrate |v(t)| here
So integrate $\int_0^5\abs{2t^2 - 12t + 6}\dd{t}$
A Lonely Bean
No
im stupid
You are gonna have to break up the interval depends on the roots
Alternatively you could take your answer from b and just add $2\int_{t_1}^{t_2}(-2t^2 + 12t - 6)\dd{t}$
hm
Where t_1 and t_2 are the roots
A Lonely Bean
I think this is easier yeah
roots of what though?
so like 0 and -110/3
0 is not a root of v(t)
Do you know how to solve that quadratic equation? v(t) = 0
Solve 2t^2 - 12t + 6 = 0 using quadratic formula or whatever method you want
yeah
.5505
and 5.449
when i get the decimals i get stumped
as she wants a pure fraction answer
So you just don't approximate, leave the roots as $3+\sqrt6$ and $3-\sqrt6$
A Lonely Bean
OHHHHHHHHHHHH
So we can now calculate $2\int_{3-\sqrt6}^{3+\sqrt6}(-2t^2 + 12t - 6)\dd{t}$
A Lonely Bean
Eh, which gets really messy unless we complete the square
So -2t^2 + 12t - 6 is the same as -2(t - 3)^2 + 12, meaning that's symmetrical around t = 3
And we can rewrite that integral as $4\int_3^{3+\sqrt6}(-(t - 3)^2 + 6)\dd{t}$
A Lonely Bean
I see it
Can you integrate this or do I continue?
Okay, don't forget that you have to add this to -110/3
thank you sm
You are welcome
The entire interval, yeah
so it means i dont need the 3+sqrt6
So, when are take the absolute value of this function, everything that is below the x-axis gets flipped around the x-axis and becomes positive
kk
In terms of the area, it stays the same except we add twice the geometric area of the part of the graph that used to be below the x-axis
That's basically what we did here
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Why are you even doing that ?
Doing which sry?
Never mind. You can do that however you have made a big blunder.
Firstly, do you think that you can simply take 1/9 out from ((u-8)/9)^5 ?
Ah yes true
oh haha
What's wrong with me? π€¦ββοΈ
No.
Firstly, du can never just be a number. π
du will always be of form (some expression)dx.
Why don't you try doing du business more systematically?
Always write u = (whatever expression you assume as u)
differentiate w.r.t. x(or whichever variable you have).
you'll get, du/dx = (some expression)
So, you have du = (some expression * dx)
Yep my lazyness is a problem
