已知sin(a+β)-cos(a+β)sina=根号3/3,cos2β=?
问题描述:
已知sin(a+β)-cos(a+β)sina=根号3/3,cos2β=?
答
sin(a+β)cosα-cos(a+β)sina=√3/3
sin[(a+β)-a]=sinβ=√3/3
cos2β=1-2(sinβ)^2=1-2/3=1/3