# Derivative of the Cosine Squared Function

In this tutorial we shall discuss the derivative of the cosine squared function and its related examples. It can be proved using the definition of differentiation.

We have a function of the form

By the definition of differentiation we have

Putting the value of the function in equation (i), we get

Using the formula from trigonometry

Example: Find the derivative of

We have the given function as

Differentiating with respect to variable $x$, we get

Using the rule $\frac{d}{{dx}}{\cos ^2}x = - 2\cos x\sin x$, we get