cos(-π/4)乘tan(-5π/6)=?

cos(-π/4)乘tan(-5π/6)=?
cos(-π/4)乘tan(-5π/6)=?

cos(-π/4)乘tan(-5π/6)=?
-π/4为第四象限角cos(-π/4)=cos(π/4)=√2/2
-5π/6为第三象限角tan(-5π/6)=tan(π-5π/6)=tan(π/6)=√3/3
cos(-π/4)*tan(-5π/6)=cos(π/4)*tan(π-5π/6)=cos(π/4)*tan(π/6)=√2/2*√3/3=√6/6

cos(-π/4)乘tan(-5π/6)=根号2\2*(-根号3\3)=-根号6\6