x^2-ax+2y-b+bx^2+3x-3y-1x^2+bx^2-ax+3x+2y-3y-b-1(1+b)x^2+(3-a)x+2y-3y-b-1要使值与字母x取值无关则1+b=0 3-a=0b=-1 a=33(a^2-ab-b^2)-(4a^2-ab+b^2)=-a^2-2ab-4b^2=-9+6-4=-7
