#help-17
1 messages · Page 164 of 1
oo why? i just glimpsed over it
based off the syllabus, ibp isn't a thing
ah
because it is overkill and you can do this directly from part i
dan note that sin^2 = 1 - cos^2
you have to* do this directly
mhm
[\int\frac{1 +\cos x}{\sin^2x},\dd x= \int \frac{1 + \cos x}{(1+\cos x)(1-\cos x)},\dd x]
maximo¹
okay so basically from the syllabus's generic solutions for any hence find this integral question
you use the derivative you find from (i) and equate that to the original y + C
??
wait dan do you know the integral of tan(x)sec(x)?
This simplifies nicely, and I assume it's the intended solution
You are using the first part to find dx
according to the syllabus nope
but it's secx + C
ok never mind what i said, redstone is right
does redstone's solution use the answer from (i)?
yes
okay so i remove the 2 from the integral
idk how to use texit so bear with me
integral of 1/(1 + cosx) = sinx/(1 + cosx) + C
uhh
ok i had a sit down and did the question, i think the easiest route by far is to try to use something very similar to the original function to differentiate into 2/1-cosx
if you want i can show you pieces of my solution?
sure
do you want the whole solution or just a hint?
just a start
this looks very similar to what we got in part i, can we try and construct a function that would work for this based on what we know?
very similar
but i don't see how you continue from here given the denominator is different
well work backwards, mess around with the minus signs a bit
you know that the denominator was v^2 via the product rule, and that v ended up cancelling out right?
so what could the new demoninator be based on that
1 - 2cosx + cos^2x
however, due to the negative that cos gives when differentiation, you may want to make the numerator negative to account for that
dont expand it !
(1 - cosx)^2..?
no, dont change the intergal any further
use part i to help, you know what the integral of 2/1+cosx is, so you can really just mess with the minus signs
instead of integrating, try differentiating something similar to the original function, and see if you can get what you got here
2/(1 - cosx)^2?
where did the sinx go?
2sinx/(1 + cosx) this was the original f(x)
mhm
but how would getting rid of sinx help
if the only difference is the signs, why would u want to get rid of trig functions completely?
to make life simpler i guess
okay so what's the follow-up after what we just did with the denominator
but then the denominator wouldnt cancel like how it did on the first time via sin^2x + cos^2x
do u want to see my full solution and then ask any questions if u have any?
sure
but how do we integrate that
well by fundamental theorem of calculus if by differentiating y you get dy/dx, then by integrating dy/dx you get y?
so you already have the answer
so the answer is 1/(cosx - 1)?
we divided it by 2
and differentiating is the exact opposite of integrating
oh yes sorry
so -sinx/1-cosx
remove a linear factor
and took out a negative sign?
no?
we ended up with -(1 + cosx)/(sin^2x)
but you already have the integral of 2/1-cosx
okay say that we have this expression that we constructed
look at this rearrangement here
how does it use any answer from (i)?
becasue we used part i to be able to deduce how to construct this function
its just 2 sign changes from part i
it's always the syllabus that restricts this from happening
we found the third line, thats the answer
what?
but yes i would say it works
i didnt use any non elementary methods
i mean, idk ur syllabus but this is usually how hence questions are solved
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what
Differentiate using the chain rule, put it equal to 0
you can really use chain rule here directly
²⁰Ne
now you can
that is what i thought
times 3 right?
so
the derivative of e^x is e^x
so
the derivative of that whole thing
e^xln(2x) * (d/dx(xln(2x))
ye
simplify x/2x to 1/2
set this whole thing equal to 0 and solve
that seems kinda stupid
divide both sides by 3 and the 3 goes away
then divide both sides by e^ln2x(x) and that goes away?
yep, thats not true, so its not a solution
but we just divided that by both sides
i was more referring to non-constant factors
is 3 a critical point?
so e^(x(ln(2x))) = 0 and (0.5 + ln(2x)) = 0
no, why would it be
we wanna find where x is 0
if i multiplied both sides by 6, would 6 be a critical point? No
how the heck do you even solve for 0 with something as complicated as that
log both sides?
extract power?
Whats e^1 equal to
e
right, so that cant be it
e^0 == 1
thats correct
so what the heck there is nothin
Correct
ahh
keep going
subtract ln2 from both sides?
keep going
So u got lnx = -0.5 - ln2
right
now lets do this
lets make a new variable b
b = -0.5 - ln2
so now we get ln(x) = b
how do we solve for x
what must we do to both sides
inverse ln?
Which is?
yes, we do e^both sides
e^b = x
yes thats what it comes to
e^(ln x) = x
and then e^b is just e^b
so x = e^b
and whats our value of b?
Back to this
look at th expoentital and logaritjmic property
lnx = -0.5 - ln2
what do we do to both sides
to get ‘x’ by itself
we just did it
just asking u to repeat
(╯°□°)╯︵ ┻━┻
whatever we do to one side, we must do to the other side too
cant just do something on one side only
but its equivalent
nope
Thats showing that e^ is the functional inverse of lnx
This is a rule u cant break in math
ur on the right track, just try again
lnx = -0.5 - ln2
whatever u did to the left side, do it to the right side too
how does that help though
now what is e^(ln(x)) equal to
simplify that
using the exponential logarithmoc property
Ur just simplifying, ur not doing e^ both sides again
Nope thats wrong
stop going to this
why don't you need ln on the right side
Stephen
i think ur issue is understanding how the functional inverse works
e^ln(x) = e^(-1/2 - ln(2))
when u get here, youve already done e^ both sides
correct?
what about the -1/2
what about it
yes
AHHH
This is a critical point
negative exponent and fractional exponent
ok yes we can use those, but first we must use quotient rule
look at the a^{x-y}
see how its just like our e^(-0.5-ln2)?
these little images with math stuff super helpful
fr
so its just 2
1/(2\sqrt(e))
solve for maxima
we need all extrema, not just maxima
But first, check if 1/2sqrte is on our interval
otherwise, its invalid
and we cant use it for extremaa
ok so this is in our interval, so we can potentially get an extreme value out of this
But hold on, we arent done yet
evaluate that into the calculator
and see what u get
4.178361968
u sure .1 gives that?
2.577911626
idk
hard to type this in calculator
ye i gotchu
max is 6 at 1
and min?
but needs to be exact
We didnt end up using the critical point 
Dont do the decimals
just do the plugged in version like u showed before
Lol
so if i replace x = with .1 its right?
i feel better now that someone way smarter than me also is confused
well lets see
im p sure thats the same answer lol
hold on
$3(2(\frac 1{2\sqrt e}))^{\frac 1{2\sqrt e}} = 3(\frac 1{\sqrt e})^{\frac 1{2\sqrt e}} = 3(\sqrt {\frac 1e})^{\frac 1{2\sqrt e}}$
Stephen
yea hold on im still trying to understand
bear with me ive only a phone keyboard lol
im on discord web version on phone
i see exactly where we went wrong
Right here
shoulda caught this earlier on
try that part again
thats crazy bro
many people just quit
ahh
man i wish i caught that
yeah that makes it a lot easier
i think i can solve the new one on my own
let me try
sure, lmk if u need help
its wrong
do u have a new problem now
factors i got are
2
e^xln(2x)
(1+ 2ln(2x))
its almost exactly the same as before
solving for 1+2ln(2x) = 0 gives me
x = 1/2\sqrt(e)
sorry if thats hard to read
I didnt get that
where did i mess up
why no 2 in front of the ln?
on which line
3rd
isn't that chain rule so it goes outside
oh
that's what i did
so ts just 1/2e
same mistake i made before
😄
thanks so much
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Sorry my last help channel dissappeared can someone help with my data man assignment, thanks!
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@noble umbra Has your question been resolved?
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Can someone explain to me how the answer is B
which one do you think it should be?
I know the answer is B. I just hope someone can explain this to me because this is the only thing on the study guide I don't know how to solve and I don't really know how to do these "Areas in Polar Coordinates" things from out of everything in the unit
wait okay now I see why
but can you explain why it's B and not D? @heavy yoke
you want to pick the right bounds so that the curve goes all the way back to where it started
in this case it would integrate only half of the curve, yes
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help meee, somebody helpppp
!status
What step are you on?
1. I don't know where to begin.
2. I have begun but got stuck midway.
3. I got an answer but I was told that it's wrong.
4. I got an answer and would like my work checked.
5. I have a question about someone else's work/solution.
6. I have completed the problem and don't need help anymore. Thank you.
7. None of the above
1
I have a general idea
I thought I had the topic but when I checked my work I found out I was wrong
show your work
I just assumed from the way it looked
can you identify the equation of this line? without the shaded area, just the line at the boundary?
I don't think I can
do you know what is the equation of the blue line, roughly?
replace all $\geq$ and $\leq$ in your options with $=$ and you get two equations of lines
artemetra
one of them will be the blue line
correct
o
why? think about it like this: the shaded area includes all values of y for which it is smaller or equal to 4x+3
no problem, if you are done, type ".close"
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Been stuck on this question
What have you tried so far?
Um using 6 as the hypotenuse and then doing a2+b2=c2
I dont know where im supposed to start because Im only given height and a base and a hypotenuse
The formula is SA=Ph+2B
I got 4.8 but now I have no idea what to do with it
surface area is just a matter of finding all of the areas of the shapes and adding them up
in this case we have two triangles (front, back) and three rectangles (bottom, left, top)
what did you get 4.8 for?
okay, so a = 4.8; what does that mean on your image? can you label the side that is 4.8 (unit??) long?
Then I square rooted it to get 4.8
yep, now find the area of each surface like hailey said
(that's not the right edge...)
Ohhhhh…
that one you already know how long it is
the pythagorean theorem applies to right triangles. can you label a right triangle in that image? color it in green for me.
those are right angles
which is a good start
but we want a right triangle
which is a 2d shape
Um 4.8 sorry im bad at labeling
that's not even part of the triangle!
didn't you use the pythagorean theorem to calculate 4.8 inches?
Yes
the pythagorean theorem applies to right triangles
considering your right triangle that you've labeled -- the green one -- which side lengths do you know?
one of them is labeled already
3.6
which side is 3.6?
okay, you could have said "the blue one" but that works
are there any other side lengths in that triangle that you know?
I dont think so maybe 6 but what would be for the other triangle
Ohhh
so knowing this, are there any other side lengths in that triangle that you know?
okay, using your words, which side lengths do you know in that triangle?
3.6
using your words
"the purple side is 7.8 inches long"
is what your answer should look like
but with different colors and numbers
How did you get 7.8?
i didn't
there's also no purple side
this is an example answer, to show you the format that i'd like you to answer in
The purple side is 3.6in
And another 3.6 because they are the same?
which other is 3.6?
okay, i think that black number you've written is referring to the vertical line in the back? that's great, but what we care about is the triangle in front
you very excitedly circled the "6 in" in the back -- why?
Because you said that it would be to same for the other triangle since
But I thought that 6 was the hypotenuse and not a side
the hypotenuse is also a side
Ohhhh
it's not a leg but it's a side
I got taught that in what ever direction the square is facing that would be the hypotenuse for the problem
well, yes, the side opposite the right angle is the hypotenuse

yes... one of the sides of the front triangle is 6 inches long
which side?
blue, orange, or green?
okay. so which side lengths do you know, in that front triangle?
the blue-orange-green one
6 and 3.6
the blue side is ___ long
the orange side is ___ long
the green side is ___ long
please fill this out
or put in ??? if you don't know
the blue side is 3.6 long
the orange side is 6 long
the green side is ? long
Would I use the Pythagorean theorem?
perhaps
the pythagorean theorem is for right triangles
do you have a right triangle?
Yes
So I would do 6squared which is 36 then
3.6 squared to get 12.96
okay, keep going...
Then add both to get 48.96
i don't think you want to do that
,calc 36 - 12.96
Result:
23.04
circumstance?
Base?
So I would add 4.8+6+3.6 to get 14.4
meyvis
Yes
i don't know which side that is
okay yes good
here
what is the length of each color? you should label them on your piece of paper
Blue =3.6
Orange =6
Green=4.8
okay, and yellow?
Yellow is 8.5
now do you have enough information to compute the area of each side?
at this point i'd like you to start keeping track of your units
blue = 3.6 inches
orange = 6 inches
green = 4.8 inches
yellow = 8.5 inches
Ok gotcha
keeping track of your units will make sure that you don't make an error
The equation for problem is SA=Ph+2B
i don't know what any of those variables mean
Now im assuming that I would be adding 3.6+6+4.8 to get 14.4
P stands for perimeter and h stands for height and B is base
okay... sure that seems fine to me
Thats the equation I received
14.4 what? 14.4 school buses? 14.4 antelopes?
Inches
okay
units
Inches
B=10.8 units
you have something like B = 1/2 b h right?
Yes
you've made a distinction between B and b
so please keep it that way
but also
UNITSS
b = 3.6 what
3.6 jellybeans??
3.6 inches
we're trying to find the area of this triangle, right?
Yes
base is the green part right?
yes
stop giving me numbers without corresponding units
they mean nothing
you can use "in" for inches
4.8in
Just making sure h=6in because we are solving for a right triangle
which side is 6in?
Orange
that is not the height of the triangle
the height of the triangle is perpendicular to the base
do you know why the area of a triangle is 1/2 b h?
Wait no sorry 8.5in
it's because it's half of a rectangle
isn't that the yellow side??
Wait no then blue would be the height
yes
B=1/2(4.8in)(3.6in)
B=8.64
B=8.64in
you can calculate the unit
notice
that you are multiplying in times in
which will not produce in
but rather in²
which is a fundamentally different unit than in, since in² measures area and in measures length
Wait so is my answer right for Base im confused?
what's Base supposed to be?
8.64in
the next time you give me numbers without units i'm leaving for 10 minutes
you multiplied 4.8 in x 3.6 in
,calc 4.8 * 3.6
Result:
17.28
which would give you 17.28 in²
Sorry I just keep forgetting to add them
do you see the little 2 up there?
Yes
in² is also called square inches
Ohhhh
Ohhhh so thats what you we’re talking about
you can also write sq in if writing ² is hard
B=8.65sq
Alright good good
yes, you found P earlier
3.6in+6in+4.8in= 14.4in
good
Ok ok great
and what's h? i think you got confused earlier because this should be the height (really the length in this case) of the prism, not the height of the triangle
Wait would it be 8.5in?
yep
Ok great
and you know B = 8.65 in²
Yes
so can you use all of that to find SA?
SA=14.4in(8.5sq)+2(14.4in)
i think you substituted in the wrong spots
are you using pencil and paper at all to keep track of what's going on here?
i hope you're not constantly scrolling through the chat
Im just keeping it in my head 🫠
don't do that
But I understand where I got
short pencil > long memory
i usually just keep a stack of printer paper near me to doodle whatever
Ok ill do that
anyway yes you seem to have substituted incorrectly, in particular i see two copies of "14.4 in"
which i don't think should be the case
you're having so much trouble keeping track of these things
Im going to just say them
P=14.4in
h=8.5in
B=8.64sq
good
where did 8.5 sq in come from?
Height
note that you can add inches and inches, and you can add in² and in² together, but if you ended up in a situation where you had like 4in + 7.3sq then you'd know something went wrong
Alright well I submitted the answer and it was correct 👍
Thank you for your time I really appreciate it!
just write stuff down
Will do
no one's going to look at it but it can help you keep track and figure out what went wrong
type .close
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Kind of confused on this
i think she messed up on step 2
since if it was perpendicular wouldnt it be opposite reciprocals ?
yeah
so i would just switch them out
like
the wrong slope with the right slope
and redo the equation with the correct slope this time
yeah
Thats all i gotta do ?
where's the x
you can't just copy the incorrect y intercept over
also -2/4 can be simplified to -1/2
i forgot to simplify
mb
wouldnt we have to change the -4 to a + 4 ?
since its a negative now
Civil Service Pigeon
I gotta dip but you should get ||y = -x/2||
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how do I figure out how to make -2 rad be in the domain 0 and 2pi
,tex for z conjugate it would be $8\cos(2)-i8\sin(2)$
jacky
jacky
I feel like I just can't visualize where -2 on the unit circle is and to try to find the angle on right domain
How many radians are there in a circle?
2pi?
Indeed
So
If you travel a full revolution of a circle to the point where you started
You've travelled 2pi rads
yes
So if you add any integer multiple of 2pi to the argument, it produces the same angle
Exactly
thanks i don't think i could've thought that way
Np!
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nox💫
what
they all have x-1
so that narrows it down to 1st and second one
correct?
so confused
so which one would it be
like how do i find out
mane
can you show@me how to do it
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How should I approach this type of questions?
Is there something like f(0)×f(1)<0, saw it in answer can't really understand
Or maybe another way to approach this question
It's a quadratic so there can be maximum two roots
Yes
So check the sign of that function when x = 0 and x = 1
If you get positive, positive or negative, negative
There must be a turning point in between, or the function was simply positive/negative all the time there
So if you get positive, negative or negative, positive
This implies there is exactly one root in [0, 1)
Oh you also have to check if x = 0 is a root cause of the closed bracket
No worries
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I understand that we are using the pigeonhole principle, however is it expecting us to write the answer in some sort of equation..?
nah you'd just write out a set and apply the principle
how is that ?
like the blueprint for these proofs is: there's a set {a,b,c,d,...} of size n, and by pigeonhole if you pick n+1 from this set there's overlap
yes that's pigeon principle but how that would apply to this problem
the set is {1,2,3,...9} for people to know
9 is max because that's how many other people there are
then 10>9 so pigeonhole and you're done
sure
can you elaborate?
idk how to, pigeonhole is usually like a 1 step proof
each person has a number 1-9
like in terms of sets how would you describe this problem
I mean I said the set already
there's a set and it's smaller than the number of people
I subscribe to feynmann quotes instead sry
what are they?
@coral glen Has your question been resolved?
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Hoping for help on this question because in class we haven’t looked at graphs yet nor intervals on integrals
how do we usually look for global and absolute maxima?
take a derivative?
y0shi
are you familiar with the fundamental theorem of calculus?
not overly derivatives were my weakness and we just moved to integrals
so basically the fundamental theorem states that:
$\frac{d}{dt}\int_{0}^{t} f(x) dx=f(t)$
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I have seen that formula before
y0shi
yep
we need to use this to find the derivative
so all we really have to do is plug in that t for x
and in our case, we’re just going to replace the t in f(x) with x
and that’ll be our F’(x)
so basically i’m trying to say $\frac{d}{dx} \int_{0}^{x} f(t)dt=f(x)$
y0shi
by the fundamental theorem of calc
okay okay
so yeah basically replace the t with the x
and to find our critical points we usually set our derivative equal to?
0
but theres no numbers just variables?
if we set $F’(x)=f(x)=0$
y0shi
what value of x gives us 0?
the graph f(x) is given to us
basically look for the x intercepts of the graph
-6,4?
6
yep
and now we have to observe how the sign changes around that point
so let’s start at -6
how does the sign change near that point?
-6 is up
yes sorry
yeah alright
so basically for endpoints
we just need to look at the right or the left of the endpoint
if F’(x) is positive to the right that means that at x=-6, there is a?
i meant to ask if it was a relative min or max
all good
min
yep that’s correct

