∫cos(3x) dx=\displaystyle\int \cos(3x)\,dx =∫cos(3x)dx=A3sin(3x)+C3\sin(3x) + C3sin(3x)+CBsin(3x)+C\sin(3x) + Csin(3x)+CC−sin(3x)/3+C-\sin(3x)/3 + C−sin(3x)/3+CDsin(3x)3+C\dfrac{\sin(3x)}{3} + C3sin(3x)+Ccheck_circleExplanationu=3xu = 3xu=3x, du=3 dxdu = 3\,dxdu=3dx. ∫cosu du/3=sinu/3\int \cos u\,du/3 = \sin u/3∫cosudu/3=sinu/3.