Question

Is `f(x)= cos(3x+(5pi)/4)` increasing or decreasing at `x=-pi/4`?

Answer 1

decreasing

Explanation:

For using the firs derivative test, first get `f '(x)= -3sin(3x+(5pi)/4)`

For `x = -pi/4, f '(-pi/4)=-3sin(pi/2)=-3`. Negative sign indicates that f(x) is decreasing at `x= -pi/4`