Consider the function $f(\theta)=|\cos\theta|+|\sin(2-\theta)|$
At which of the following points is $f$ not differentiable ?
1.$\{(2n+1)\frac{\pi}{2} : n \in Z\}$
2.$\{n\pi :n \in Z\}$
3.$\{n\pi+2 : n \in Z\}$
4.$\{\frac{n\pi}{2} :n \in Z\}$
How to solve this problem, please help