e的3x次方乘以cos(2x—六分之π)的导函数怎么求?

y=(e^3x)cos(2x-π/6)的导函数怎么求?
y′=(e^3x)′cos(2x-π/6)+(e^3x)[cos(2x-π/6)]′
=（3e^3x)cos(2x-π/6)-2(e^3x)sin(2x-π/6)
=(e^3x)[3cos(2x-π/6)-2sin(2x-π/6)]