We want intsin^5xdx∫sin5xdx
Rewrite the integrand as sinx(sin^2x)^2sinx(sin2x)2:
intsinx(sin^2x)^2dx∫sinx(sin2x)2dx
Recall the identity sin^2x+cos^2x=1sin2x+cos2x=1. The identity also tells us that
sin^2x=1-cos^2xsin2x=1−cos2x
intsinx(1-cos^2x)^2dx∫sinx(1−cos2x)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)−∫(1−u2)2=−∫(1−2u+u2)
Integrate:
-int(1-2u+u^2)=-(u-u^2+1/3u^3)+C=u^2-u-1/3u^3+C−∫(1−2u+u2)=−(u−u2+13u3)+C=u2−u−13u3+C
Rewriting in terms of xx yields
intsin^5xdx=sin^2x-sinx-1/3sin^3x+C∫sin5xdx=sin2x−sinx−13sin3x+C