（cos2α）/sin（α-π/4）=-根号下2/2,则cosα+sinα的值
问题描述：
（cos2α）/sin（α-π/4）=-根号下2/2,则cosα+sinα的值
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(...