y=1/2+1/2cos2x+1/2sin2x
=1/2(sin2x+cos2x)+1/2
=√2/2(√2/2sin2x+√2/2cos2x)+1/2
=√2/2sin(2x+π/4)+1/2
sin(2x+π/4)∈[-1,1]
所以y的值域为[1/2-√2/2,1/2+√2/2]