由题意,得:
-b/2a=1,所以:b=-2a.
抛物线解析式可化为:
y=ax^2-2ax+c.
把X=-1,X=2分别代入解析式,得:
y1=a+2a+c=3a+c.
y2=4a-4a+c=c
因为a