y=x²-3x+2
=（x-3/2）^2+2-9/4
=(x-3/2)^2-1/4
y=x²-3x+2=0
x=2 x=1
顶点坐标(3/2,-1/4)
x轴的交点坐标(2,0)(1,0)
对称轴x=3/2