11. f(x) = sinx + cosx, 0<= x <= 2pie

a) Find the intervals on which f is increasing or decreasing.

b) Find the local max and min values of f.

c) Find the intervals of concavity and the inflection points

I differentiated the equation to get f'(x) = cosx - sinx and then solved for the critical value which was pie / 4 but I dont know where do go from here.