y=(x+b/2a)^2+(4ac-b^2)/4a
x=-1,y=2代入
-b/2a=-1 b=2a
(4ac-b^2)/4a=(4ac-4a^2)/4a=c-a=2 c=a+2
b=2a c=a+2代入a+b+c+2=0
a+2a+a+2+2=0
4a=-4 a=-1
b=-2 c=1
抛物线解析式为y=-x^2-2x+1