已知：sin(α+π/3)+sinα=负5分之4根号3 α∈（-π/2,0）求cosα
问题描述：
已知：sin(α+π/3)+sinα=负5分之4根号3 α∈（-π/2,0）求cosα
答
sin(α+π/3)+sinα=-4√3/5sinαcosπ/3+cosαsinπ/3+sinα=-4√3/53/2*sinα+√3/2*cosα=-4√3/53/2*sinα=-√3/2*cosα-4√3/5两边平方9/4*sin²α=9/4(1-cos²α)=3/4*cos²a+12/5*cosx+48/25cos&...