若cos2a/sin(a-π/4)=k,a为第一象限角 则sina-cosa 的值为多少如上,求解答

若cos2a/sin(a-π/4)=k,a为第一象限角 则sina-cosa 的值为多少如上,求解答 tan(a+π/4)=k,则cos2a= tan(a+π/4)=k,则cos2a=? 若sin(a-π/4)/cos2a=-根号2,则sina+cosa= 若cos2a/sin(a-π/4)=-√2/2,则cosa+sina等于多少? 若cos2a/sin((a-(π/4))=-(√2)/2,则cosa+sina的值为 若 cos2a/sin（a-π/4)= -√2/2,求cosa+sina的值. 若((cos2a)/(sin(a+(π/4))))=-√2/2则cosa-sina的值是 证明：2sin(π/4+a)sin(π/4-a)=cos2a 求证：2sin(π/4+a)sin(π/4-a)=cos2a sin(π/4+a)sin(π/4-a)=1/6求cos2a 若a∈(π/2,π),3cos2a=sin(π/4-a),则sin2a的值 若a(0,π/2),且sin^2 a+cos2a=1/4 则tana的值等于 若a属于（0,π/2）,且sin²a+cos2a=1/4,则tana的值等于 tan(a+π/4)=2,则cos2a+3sin^2a+tan a= 若cos2a=a,则sin*4a+cos*4a=? 已知sin（a-π）=3/5,求cos2a sin(a-π)=3/5求cos2a的值