I'm given these two questions from a friend today, and i don't know how to solve them at all.

4 cos4xsin4x+1=0

where the range is -3pi ≤ x ≤ 2 pi

All i know is that you're suppose to subsitute the 4x as x

and thats basically it. any help?

The second question i got was proofing Ids

(Root(2)/2) ( cos pi/12 - sin pi/12) = 1/2

How am i suppose to solve that?

Thank you so much for helping me :]