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 解析看不懂?免费查看同类题视频解析查看解答 ...