SINα=2/3 则COS(π-2α)=?
问题描述：
SINα=2/3 则COS(π-2α)=?
答
sinα=2/3
cos(π-2α)=-cos2α=-[1-2(sinα)^2]=-1+2(sinα)^2=-1+2*(2/3)^2=-1+8/9=-1/9
答
COS(π-2α)=2(sina)^2-1
SINα=2/3 COS(π-2α)=-1/9