integrate (3x + 1) * cos 2x dx
По частям u=[b]3x+1[/b] du=[u]3dx[/u] dv=cos2x dx v=[blue](1/2)sin2x[/blue] ∫ (3x+1)*cos2xdx=[b](3x+1)[/b]*(1/2)*sin2x - ∫[blue] (1/2)sin2x[/blue] * [u]3dx[/u]=(1/2)*(3x+1)*cos2x-(3/2)*(1/2)*(-cos2x)+C