Trigometric derivatives max and min - can someone show me how to do this correctly? Bruh can you just accept my question it's not for marks :(

Determine the EXACT maximum and minimum values of f (x) = 2cos x - cos 2x for 4.) 31. (5 v marks) OSXS -7. f ( x) = 2cosx - cos 2x : 2 sinx CoSx f ' ( x ) = - 2vinz+ sin 2x .2 = - 2 Jinx + 2Jin 2xx = 2sinx - 4sinxcosx ... = 2sim 2 c - 2 sink it = 2 sin ( 20c( x ) factor like that