[sinx] = 0 in x = [0,pi/2) U (pi/2,pi]
= 1 in x = pi/2
= -1 in x = (pi,2pi)
[cosx] = 1 in x = 0
= 0 in x = (0, pi/2]
= -1 in x = (pi/2, 3pi/2)
= 0 in x = [3pi/2, 2pi]
So [sinx]=[cosx] when x = (0,pi/2) U (pi/3pi/2)
The rest points are decided by periodicity