1. The problem statement, all variables and given/known data f(x)=x — cosx, 0 ≤ x ≤ 2∏ 2. Relevant equations 3. The attempt at a solution I took the derivative of the function: f'(x)=1+ sinx, 0 ≤ x ≤ 2∏ I don't know how to determine whether it is increasing or decreasing between the interval given. What should I do?