cos（2A）/sin（A-(pi/4)）=-(√2)/2
=>cosA^2-sinA^2=-(√2)/2*[sinAcos(-pi/4)+cosAsin(-pi/4)]
=>(cosA+sinA)(cosA-sinA)=-(√2)/2*[(√2)/2*sinA-(√2)/2*cosA]
=>(cosA+sinA)(cosA-sinA)=1/2(cosA-sinA)
=>cosA+sinA=1/2