Im having a difficult time figuring out what to do when asked to find critical numbers of trig functions.

I understand question such as number (1) in my picture, but im stumped at questions like (2).

Do i have to simply cos(x)-sin(x) using trig identities? Or do i just set cos(x)=0 and -sin(x)=0 and solve?

Any idea what i should review in my trig books to understand these questions better?

Thanks for the help.