differentiate sin(3x)
Let's differentiate: ddx(sin(3x))
Apply the differentiation rule: ddx(sin(f)) = ddx(f)·cos(f) with f = 3x
ⓘ The derivative of sin(x) is cos(x): ddx(sin(3x)) = ddx(3x)·cos(3x)
ddx(3x)·cos(3x)
ⓘ A constant factor stays in front of the derivative: that of ku is k·u': ddx(3x) = 3
▶Derivative:   3·cos(3x)