（x*x+ax-2y+7)-(bx*x-2x+9y-1)
=x^2+ax-2y+7-bx^2+2x-9y+1
=(1-b)x^2+(a+2)x-11y+8的值与x取值无关
1-b=0
b=1
a+2=0
a=-2
所以 a=-2,b=1