cos13π/6=cos(2π+π/6)=cos(π/6)=√3/2几道题目都是同样答案？sin(-4π/3)=sin(-2π+2π/3)=sin(2π/3)=sin(π-π/3)=sin(π/3)=√3/2;cos(-79π/6)=cos(79π/6)=cos(12π+7π/6)=cos(7π/6)=cos(π+π/6)=-cos(π/6)=-√3/2