若cos2a/sin（a-π/4)=-√2/2,求cosa+sina的值.

问题：若cos2a/sin（a-π/4)=-√2/2,求cosa+sina的值.

答案：↓↓↓

姜超的回答：

网友采纳　　cos2a/sin（a-π/4)=-√2/2,sin(π/2-2a)/sin（a-π/4)=-√2/2,-sin(2a-π/2)/sin（a-π/4)=-√2/2,[-2sin（a-π/4)cos（a-π/4)）/sin（a-π/4)=-√2/2,-2cos（a-π/4)）=-√2/2,-2[cosacosπ/4+sina...