Question

How do you find the derivative of `(cosx)(sinx)`?

Answer 1

Use the product rule:
`d/dx (cosx) *sinx +d/dx (sinx) *cosx`
`=-sinx *sinx +cosx *cosx`
`=cos^2x-sin^2x`

The answer could also take the form `2cos^2x -1` arriving at this answer involves the use of trigonometric identities.