Question: y=x^2 SIN (3x)

Question

y=x² sin(3x)

= 2x SIN (3x) + x^2 (3cos(3x)) ---> i'm confused how to get the 3 in front of cos

= 2x SIN (3x) +3x^2 cos (3x)

Answer 1

By the Chain Rule, the derivative of sin(3x) is cos(3x)(3x)' = 3cos(3x).

Answer 2

3 is a factor. By the commutative property of multiplication it can be moved.

(x²)(3)(cos 3x)

(3)x²(cos 3x)