An equation like is called an identity because it holds for all values of θ. An equatio...

An equation like is called an identity because it holds for all values of θ. An equation like is not an identity because it holds only for selected values of θ, not all. If you differentiate both sides of a trigonometric identity in θ with respect to θ, the resulting new equation will also be an identity.

Differentiate the following to show that the resulting equations hold for all θ.