In the following Laplace transform, how do you get rid of the cos(2at)*sin(at)?

L{sin^3 (at)}
L{ sin(at) * [1/2 ( 1 - cos(2at)]}
1/2 L{sin(at)} - 1/2 L{cos(2at)*sin(at)}
1/2 * (a^2)/(s^2 + a^2) - 1/2 L{cos(2at)*sin(at)}