sin2a=3/5 → cos2a=4/5,∴ sina=√(1-cos2a)=√(1-4/5)=√5/5,cosa=2√5/5；[2cos²(a/2)-sina-1]/[√2sin(a+π/4)]=(cosa+1-sina-1)/(cosa+sina)=(2√5/5-√5/5)/(2√5/5+2√5/5)=1/3；