cos(7π/2-α)等于sin多少
问题描述：
cos(7π/2-α)等于sin多少
答
cos(2kπ+α)=cos α
cos(π/2-α)=sin α
cos(π/2+α)=-sin α
cos(-α)=cos α
cos(π+α)=-cos α
cos(π-α)=-cos α
哎 我也不想算了 带进去吧