Trigonometric Integral Homework: Solving \int (sin^6(x))(cos^3(x))

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Homework Help Overview

The discussion revolves around solving the integral \(\int 41(\sin^{6}(x))(\cos^{3}(x)) \, dx\), which falls under the subject area of trigonometric integrals. Participants explore various methods and substitutions to approach the problem.

Discussion Character

  • Mixed

Approaches and Questions Raised

  • Participants suggest using substitution, specifically \(u = \sin(x)\), and discuss the implications of using half-angle identities and integration by parts. There are attempts to clarify the handling of powers of sine and cosine, particularly when one power is odd.

Discussion Status

The conversation includes multiple interpretations of the problem, with some participants expressing confusion and seeking guidance. Others provide hints and encouragement to work through the integral, indicating a collaborative atmosphere. While some participants have made progress, there is no explicit consensus on the final approach or solution.

Contextual Notes

Participants mention feeling lost due to the recent introduction of the topic in class and the lack of teacher support. There is also a note of urgency as some participants balance this problem with other coursework.

Mugen Prospec
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Homework Statement




[tex]\int[/tex] 41(sin[tex]^{6}[/tex](x))(cos[tex]^{3}[/tex](x))


Homework Equations





The Attempt at a Solution



I think you are supposed to use the half angle identities and then maybe integration by parts but I am lost on it.
 
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how about starting by trying the substitution u = sinx
 
I have tried a few different things, more than I wanted to list but it just keeps getting more and more convoluted. I need a walk through we just started this in class and my teacher doesn't answer questions so I am just a bit lost over all.
 
You don't have to do anything complicated with it, cos(x)dx=d(sin(x)). Just substitute u=sin(x). There are rules for dealing with powers of sin's and cos's. They are particularly easy if one power is odd.
 
Dick said:
You don't have to do anything complicated with it, cos(x)dx=d(sin(x)). Just substitute u=sin(x). There are rules for dealing with powers of sin's and cos's. They are particularly easy if one power is odd.

Ok I know what your talking about. It was just in our chapter about integration by parts so I was a little first sight shocked. Can some one give me an answer so when I complete it I can know if I am correct or not.
 
Oh, come on. Just work it out and show us what you get. I'll guarantee someone will check it.
 
Dick said:
Oh, come on. Just work it out and show us what you get. I'll guarantee someone will check it.

Ok I have other work to do this one has bee on my mind all night. Ill post it tomorrow when I am clear of thought
 
Mugen Prospec said:
Ok I have other work to do this one has bee on my mind all night. Ill post it tomorrow when I am clear of thought

It's REALLY easy with the substitution lanedance suggested. You might want to clear your mind on this one and go to bed happy. But tomorrow is ok too.
 
Ok thanks a lot Ill see what I can do tonight.
 
  • #10
Free hint since you are playing along: cos^2(x)=1-sin^2(x)=(1-u^2).
 
  • #11
ok i got
41(sin^7(x)/7)(1/2 x + 1/4sin2x+c)
 
  • #12
doesn;t look quite right to me, maybe show your working
 
  • #13
Thats what I was thinking. after using u substitution I was left with

(u)^6 (cos^2(x)) cos(x) du/cos(x)

So cos(x) canceled out.
 
Last edited:
  • #14
Mugen Prospec said:
Thats what I was thinking. after using u substitution I was left with

(u)^6 (cos^2(x)) cos(x) du/cos(x)

So cos(x) canceled out.

Fine. Now what's cos^2(x) in terms of u?
 
  • #15
Oh ok the identity. so now all turns into
u^7 (1-u^2) du
Do I do their antiderivative now? And then substitute sin(x) back in. I am not sure if you can do each of there AD since they are multiplying one another.
 
  • #16
Mugen Prospec said:
Oh ok the identity. so now all turns into
u^7 (1-u^2) du
Do I do their antiderivative now? And then substitute sin(x) back in. I am not sure if you can do each of there AD since they are multiplying one another.

Of course you don't take the AD of each one. That's wrong. You multiply it out.
 
  • #17
OK that what I thought I am trying to do this not without witting it down since I am in chemistry.
So we get (u^6)-(u^8)du
then (u^7)/7) - (u^9)/9)
41 (sin^7(x))/7) - (sin^9(x))/9)
is that it maybe?
 
  • #18
Mugen Prospec said:
OK that what I thought I am trying to do this not without witting it down since I am in chemistry.
So we get (u^6)-(u^8)du
then (u^7)/7) - (u^9)/9)
41 (sin^7(x))/7) - (sin^9(x))/9)
is that it maybe?

You are missing a parenthesis level following the 41, but yes, that's it.
 
  • #19
Ok awesome thank you for you patience.
 

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