# Is #f(x)= 4xcos(3x-(5pi)/4) # increasing or decreasing at #x=-pi/4 #?

##### 1 Answer

Jun 2, 2017

Increasing.

#### Explanation:

The derivative can tell you where an original function is increasing or decreasing. If the derivative is positive at your point of interest, then the original function is *increasing* at that point. If the derivative is negative at your point of interest, then the original function is *decreasing* at that point.

**Step 1.** Determine the derivative of

Requires the product rule

**Step 2.** Determine if

At the value *positive*, which means that the original function,