Question

What is the derivative of `cos(xy)`?

Answer 1

`d/(dx) cos(xy) = -(y+x(dy)/(dx))sin(xy)`

Explanation:

Use the chain rule:

`d/(dx) cos(xy) = -sin(xy) *d/(dx) (xy)`

then the product rule:

`-sin(xy) *d/(dx) (xy) = -sin(xy) (y+x(dy)/(dx))`