y=2x²-4x-1
y=2(x-1)^2-3

对称轴x=1
顶点(1,-3)
2(x-1)^2-3=0
(x-1)^2=3/2
x-1=±√6/2
x=1±√6/2

交点坐标(1-√6/2,0)(1+√6/2,0)