Hi, I need to integrate cos^3(x).

So far I have:∫cos^3(x) = ∫cos(x)(1-sin^2(x)) = ∫cos(x) -∫cos(x)sin^2(x)= sin(x) - (1/3) sin^3(x) = 1/3 (3sin(x) - sin^3(x))

How do I get from this to: 1/12 (9sin(x) + sin(3x))

Is there a special trig identity?

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- Aug 20th 2009, 03:23 AMMr.Reeintegral of cos^3(x)
Hi, I need to integrate cos^3(x).

So far I have:∫cos^3(x) = ∫cos(x)(1-sin^2(x)) = ∫cos(x) -∫cos(x)sin^2(x)= sin(x) - (1/3) sin^3(x) = 1/3 (3sin(x) - sin^3(x))

How do I get from this to: 1/12 (9sin(x) + sin(3x))

Is there a special trig identity? - Aug 20th 2009, 04:32 AMmr fantastic