|2(cosx)^2-1|=sinx
|1-2(sinx)^2|=sinx
1-2(sinx)^2=±sinx
(i)1-2(sinx)^2=sinx
2(sinx)^2+sinx-1=0
sinx=-1或1/2
所以x=3π/2或π/6或5π/6
(ii)1-2(sinx)^2=-sinx
2(sinx)^2-sinx-1=0
sinx=1或-1/2
所以x=π/2或7π/6或11π/6
所以解集是{π/6,π/2,5π/6,7π/6,3π/2,11π/6}