解 f(x)=x^2 + (a+1)x + b
开口向上,对称轴为 -(a+1)/2
因为f(-1) = 0 所以 -(a+1)/2 = 1
f(1) = a + b + 2 > 1 a + b > -1
f(-1) = b - a = 0 b = a
2a > -1
综上所述
a >= 1