(cosα-cosβ)^2+(sinα-sinβ)^2=4/5
问题描述:
(cosα-cosβ)^2+(sinα-sinβ)^2=4/5
(1)cos(α-β)的值
(2)若-π/2<β<0<α<π/2 且sinβ=-5/13 求sinα
答
2-2(cosαcosβ+sinαsinβ)=4/5,即2-2cos(α-β)=4/5