sina=sin[(a-π/3)+π/3]
=sin(a-π/3)cosπ/3+cos(a-π/3)sinπ/3
=1/2*sin(a-π/3)+根号3/2cos(a-π/3)
=1/6+根号3/2cos(a-π/3)
应该给出a的范围
如果没有就有两种情况
cos(a-π/3)=2根号2/3或cos(a-π/3)=-2根号2/3
代入即可