问题描述: (cos2α)/sin(α-π/4)=-根号下2/2,则cosα+sinα的值 1个回答 分类:数学 2014-10-04 问题解答: 我来补答 因为 cos2α=sin(π/2-2α)=sin2(π/4-α)=2sin(π/4-α)cos(π/4-α)所以 (cos2α)/sin(α-π/4)=- (cos2α)/sin(π/4-α)=-2cos(π/4-α)=-√2/2所以 cos(π/4-α)= √2/4即cos(π/4)cosα+sin(π/4)sinα=√2/4(√2/2)cosα+(√2/2)sinα=√2/4从而 cosα+sinα=1/2 展开全文阅读