∫sin^4 3x dx 怎么求?
2个回答

∫sin^4 3xdx

=∫(1-cos6x)^2/4 dx

=1/4∫1+cos^2 6x-2cos6x)dx

=1/4(∫dx+∫(1+cos12x)/2 dx -2∫cos6xdx)

=1/4(x+1/2x+1/6sin12x-1/3cos6x)

=3/8x+1/24sin12x-1/12cos6x +C