若sin^2β-sin^2α=m,则sin(α+β)sin(α-β)
问题描述：
若sin^2β-sin^2α=m,则sin(α+β)sin(α-β)
答
sin^2β-sin^2α=m所以（1-cos^2β)-（1-cos^2α)=m得打cos^2α-cos^2β=m所以cos^2α=m+cos^2βsin^2α=sin^2β-msin(α+β)sin(α-β)=sin^2αcos^2β-cos^2αsin^2β=(sin^2β-m)cos^2β-(m+cos^2β)sin^2β=-m...