y=a-bcos(2x+π/6）,3/2=a+b , -1/2=a-b , a=1/2 , b=1
gx=-2sin（x-π/3）在区间（-π/2,π/2）上的最值

x-π/3=-π/2 , x=-π/6 g(x)取得最大值=2
2kπ-π/6