Solution for cos^3 x dx.

  • #1
PrudensOptimus
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OK, I know the solution for cos^3 x dx is sinx - sin^3 x / 3 + C.


And that

you basically solve

integral of cosx*(1-sin^2x) dx. to get it.

but,...

what I don't get is how do you solve cosx*(1-sin^x) dx... is there a trick that I didn't get from the parts formula?
 

Answers and Replies

  • #2
Hurkyl
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It would help if you mentioned you're trying to integrate!

Distribute the multiplication and see if that gives you any hints.
 
  • #3
HallsofIvy
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Yes, one doesn't normally say "solve f(x)dx"!

Hurkyl, I don't see any reason to "distribute" (multiply out) anything. There is an obvious substitution for ∫(1- sin2(x))cos(x)dx.
 
  • #4
Hurkyl
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Good point. :smile:
 
  • #5
PrudensOptimus
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I have never learned integration by parts. Please help me.
 
  • #6
Hurkyl
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But, I presume, you know substitution?
 
  • #7
PrudensOptimus
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Nope, any products in Integrals other than those constants are new to me.
 
  • #8
Hurkyl
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I didn't ask about products, I asked about substitution!


E.G. would you know how to integrate ∫ sin(πx) dx
 
  • #9
PrudensOptimus
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i know the answer,

but I don't know the part when they did the dx = dv(ax) part... that confuzed me.
 
  • #10
ShawnD
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Ok well here's how I worked it out

http://myfiles.dyndns.org/pictures/integrate1.jpg

I put a few steps together but you can still see what happened sort of.
 
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