What is the integral of sin^5(x)sin5(x)?

1 Answer
Mar 30, 2018

intsin^5xdx=sin^2x-sinx-1/3sin^3x+Csin5xdx=sin2xsinx13sin3x+C

Explanation:

We want intsin^5xdxsin5xdx

Rewrite the integrand as sinx(sin^2x)^2sinx(sin2x)2:

intsinx(sin^2x)^2dxsinx(sin2x)2dx

Recall the identity sin^2x+cos^2x=1sin2x+cos2x=1. The identity also tells us that

sin^2x=1-cos^2xsin2x=1cos2x

intsinx(1-cos^2x)^2dxsinx(1cos2x)2dx

This can be solved using a simple substitution. Let

u=cosx, du=-sinxdx, -du=sinxdxu=cosx,du=sinxdx,du=sinxdx

Rewrite the integral:

-int(1-u^2)^2=-int(1-2u+u^2)(1u2)2=(12u+u2)

Integrate:

-int(1-2u+u^2)=-(u-u^2+1/3u^3)+C=u^2-u-1/3u^3+C(12u+u2)=(uu2+13u3)+C=u2u13u3+C

Rewriting in terms of xx yields

intsin^5xdx=sin^2x-sinx-1/3sin^3x+Csin5xdx=sin2xsinx13sin3x+C