把 x=-2 代入原方程,得:
16a^2 - 8a + b - 8 = 0
则 b = -16(a^2 - a/2 - 1/2) = -16[(a - 1/4)^2 - 9/16]
因为 (a - 1/4)^2 >= 0,所以 [(a - 1/4)^2 - 9/16] >= -9/16,所以,16[(a - 1/4)^2 - 9/16] >= -9
则有 b