已知sin(3π/2+α)=1/3,则cos(π-2α)=?
问题描述：
已知sin(3π/2+α)=1/3,则cos(π-2α)=?
答
sin(3π/2+α)=-cosa=1/3;
cosa=-1/3;
cos(π-2α)=-cos2α=1-2(cosα)^2=1-2/9=7/9
答
sin(3π/2+α)=1/3
因为3π/2+α在第4象限
所以sin(3π/2+α)=-cosa=1/3
cosa=-1/3
cos(π-2α)=-cos2a=1-2(cosa)^2=1-2*1/9=7/9
答
sin(3π/2+α)=1/3
因为3π/2+α在第4象限
sin