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

In summary: I appreciate it.In summary, the given integral can be solved using the substitution u=sin(x) and the half angle identities to simplify the expression. The final result is 41(sin^7(x)/7)-(sin^9(x)/9).
  • #1
Mugen Prospec
42
0

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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  • #2
how about starting by trying the substitution u = sinx
 
  • #3
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.
 
  • #4
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.
 
  • #5
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.
 
  • #6
Oh, come on. Just work it out and show us what you get. I'll guarantee someone will check it.
 
  • #7
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
 
  • #8
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.
 
  • #9
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.
 
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  • #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.
 

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

What is a trigonometric integral?

A trigonometric integral is an integral that involves trigonometric functions, such as sine, cosine, and tangent. These types of integrals are commonly used in calculus to solve problems in geometry, physics, and engineering.

What is the process for solving a trigonometric integral?

The process for solving a trigonometric integral involves using various integration techniques, such as substitution or integration by parts, as well as trigonometric identities. The goal is to manipulate the integral into a form that can be easily integrated using standard methods.

How do you solve the integral of (sin^6(x))(cos^3(x))?

To solve this specific trigonometric integral, you can use the half-angle formula for cosine to rewrite the integral as a combination of sine and cosine terms. Then, you can use the power-reducing formula for sine to simplify the integral further. Finally, you can use basic integration techniques to solve the remaining integral.

What are the common mistakes to avoid when solving trigonometric integrals?

Common mistakes when solving trigonometric integrals include not properly applying trigonometric identities, forgetting to use substitution or integration by parts, and making errors in algebraic simplification. It is important to carefully follow the steps and check your work to avoid these mistakes.

How can I practice and improve my skills in solving trigonometric integrals?

The best way to practice and improve your skills in solving trigonometric integrals is to work through a variety of practice problems, both in your textbook and online. You can also review trigonometric identities and integration techniques to strengthen your understanding. Seeking help from a tutor or attending study groups can also be beneficial.

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