Find the absolute max and absolute min values of f on the given interval.

1. f(t) = 2 cost + sin 2t, interval [0, pie/2]

2. f(t) = x - ln x , [1/2, 2]

For #1, I figured out the f '(t) which is -sin t + cos 2... I don't know if this is correct. the question is how do I find the critical pts with this f '(t)? Same question for #2. The f '(t) that I figured out is 1/x... How do I find the critical pts? Thanks for your help.