cos2x=2(cosx)^2-1,∴1+cos2x=2(cosx)^2,sin(π/2+x)=cosx,∴(1+cos2x)/4sin(π/2+x)=2(cosx)^2/4cosx=(1/2)cosxcos(π-x/2)=cos(x/2),∴sin(x/2)cos(π-x/2)=sin(x/2)cos(x/2)=(1/2)sinxy=(1/2)cosx-a(1/2)sinx=(√...