已知cos(π/3+α)=1/4,α为第三象限角,求cos(3π/2—α)+sin(α—3π/2)的值

Question

已知cos(π/3+α)=1/4,α为第三象限角,求cos(3π/2—α)+sin(α—3π/2)的值

Answer 1

cos(π/3+a)=1/4
cosπ/3cosa-sinπ/3sina=1/4
1/2cosa-根号3/2sina=1/4
cosa-根号3sina=1/2-----(1)
又α为第三象限角
则sina