sin(2x)-sin(x)= 0 

2sin(x)cos(x)-sin(x)= 0

sin(x)(2cos(x)-1)= 0

1. sin(x)= o

x = pi×n

2. 2cos(x)-1=0

cos(x) = 1/2

x=+-arccos(1/2)+2×pi×N

x=+-pi/3+2×pi×N