integral 24 cos^2 3x dx

ubah terlebih dahulu cos^2(3x) = 1/2 + 1/2 cos(2*3x) = 1/2 + 1/2 cos(6x)
sehingga, diperoleh
\int[24 cos^2(3x)]dx = \int[24 (1/2 + 1/2 cos(6x))]dx = \int[12 + 12 cos(6x)]dx = 12x + 12/6 sin(6x) + C = 12x + 2 sin(6x) + C