# Is #f(x)= x-12sin(3x-pi/4) # increasing or decreasing at #x=-pi/6 #?

##### 1 Answer

Dec 1, 2015

It's decreasing.

#### Explanation:

The answer lies in the first derivative: if it is positive at

So, the first derivative is

Evaluate at

which is clearly negative. So, the function is decreasing, as you can see in the graph.