How do you integrate int sin^3xsin3x by integration by parts method?

1 Answer
Aug 2, 2016

=1/3 cos^3 - cos x + C=13cos3cosx+C

Explanation:

int \ sin^3 x \ dx

= int \d/dx (-cos x) sin^2 x \ dx

which by IBP

=-cos x sin^2x + int \cos x d/dx( sin^2 x) \ dx

=-cos x sin^2 x + 2 int \cos^2 x sin x \ dx

=-cos x sin^2 x + 2 int \d/dx ( - 1/3 cos^3 x) \ dx

=-cos x sin^2 x - 2/3 cos^3 x + C

=-cos x (1 - cos^2 x) - 2/3 cos^3 x + C

=-cos x + cos^3 x - 2/3 cos^3 x + C

=1/3 cos^3 - cos x + C