Question

已知sin(α+β)sin(β-α)=m，则cos²α-cos²β等于(    )

A.-m           B.m            C.-4m            D.4m

Answer 1

解析：cos²α-cos²β=(1+cos2α)(1+cos2β)=

=-sin(α+β)sin(α-β)=sin(α+β)sin(β-α)=m.

答案：B