f(x)=sin^2x+cos^2x+2sinxcosx+cos2x-1
=1+sin2x+cos2x-1
=sin2x+cos2x
=√2(sin(2x+π/4))
2x+π/4=π/2+kπ
2x=π/4+kπ
x=π/8+kπ/2
对称轴方程即为x=π/8+kπ/2（k∈Z）