①:已知sin(π+α)=-1/3,求cos(5π+α)的值;②:已知sin(π/3+α)=-1/2,求sin(α-5π/3)的值.
问题描述:
①:已知sin(π+α)=-1/3,求cos(5π+α)的值;②:已知sin(π/3+α)=-1/2,求sin(α-5π/3)的值.
答
cos(5π+a)=cos(π+a)=+ - 2根号2/3
sin(a-5π/3)=sin(a-5π/3+2π)=sin(a+π/3)=-1/2