sin ^2 2a+sin 2acos 2a-cos 2a=1; sin 2acos 2a-cos 2a=1-sin ^2 2a=cos^2 2a ; sin 2a-1=cos 2a,或cos 2a=0; 当cos 2a=0时,a=π/4;则tan a=1.; 当sin 2a-1=cos 2a时,sin2a+cos2a=1; √2sin(2a+π/4)=1; sin(2a+π/...