(1)f（x）=2sin x cos x +cos 2x=sin2x+cos2x=√2sin(2x+π/4)∴f(π/2)=√2sin(π+π/4)=-√2sinπ/4=-1(2)f(a/2)=√2sin(a+π/4)=√2/2∴sin(a+π/4)=1/2∵0＜a＜π∴π/4＜a+π/4＜5π/4∴a+π/4=5π/6∴cos(a+π...