Question

Is `f(x)= cot(3x+(3pi)/8)` increasing or decreasing at `x=pi/12`?

Answer 1

`f'(pi/12)=-12/(2+sqrt(2))<0`

Explanation:

We get

`f'(x)=-3sec^2(pi/8-3x)`
so
`f'(pi/12)=-12/(2+sqrt(2))<0`