how do I solve 4cosxsinx=1?

4cosx sinx = 1

Do you know the identity sin(2x) = 2cos(x)sin(x) ?

Well, use that here.

4cos(x) sin(x) = 1

2(2cos(x) sin(x)) = 1

2sin(2x) = 1

Can you continue now? Post your answer :)