Use the product rule (uv)' = u'v + uv', with u = 3x and v = sin(x) such that uv = 3xsin(x).Originally Posted bymortoleeuk

Then u' = 3 and v' = cos(x).

Thus u'v = 3sin(x) and uv' = 3xcos(x).

Thus dy/dx = (uv)' = u'v + uv' = 3sin(x) + 3xcos(x).