(2x^2+ax-y+6)-(2bx^2-3x+5y-1) =2x^2-2bx+ax+3x-6y+7 =2(1-b)x^2+(a+3)x+(7-6y) 因为代数式(2x^2+ax-y+6)-(2bx^2-3x+5y-1)的值与字母x的取值无关,所以 1-b=0,b=1.a+3=0,a=-3.所以(a+b)(a-b)＝a^2-b^2=8...