# Is #f(x)=cos(-x)# increasing or decreasing at #x=0#?

##### 1 Answer

Apr 6, 2018

#### Explanation:

The first derivative provides the slope at each point of our function. A positive slope means the function is increasing and that a negative slope means that the function is decreasing.

Knowing this, we can find out if

Before starting, we may want to simplify our function. Because

Evaluate at

In this case, the slope is neither negative or positive, but 0. Hence,