2-2sin（a+3π/4）cos（a+π/4）=2-2sin(π/4-a)cos(a+π/4)=2-2cos(π/2-(π/4-a))cos(a+π/4)=2-2[cos(a+π/4)]^2=2[sin(a+π/4)]^2=1-cos(2a+π/2)=1+cos(π/2-2a)=1+sin2a=(sina+cosa)^2cosa-sina[2-2sin(a+3π/...