f(x) = 2x^2 + bx + 1 = x,2x^2 + (b-1)x + 1 = 0.(b-1)^2 - 8 > 0,(b-1)^2 > 2*2^(1/2)b > 1 + 2^(3/2)或b < 1 - 2^(3/2).设g(x) = f(x) - x = 2x^2 + (b-1)x + 1曲线g(x)是开口向上的抛物线.（2）|x2 - x1| < 2,4 ...