(1) x1 < 0,x2 < 0,x1 + x2 = -2(m-1) < 0,m > 1
x1*x2 > 0,x1*x2 = 2m-3 > 0,m > 3/2
即m > 3/2
(2) 顶点到x轴的距离等于2m-3
y=x^2+2(m-1)x+2m-3 = (x + 1)(x + 2m -3)
x1 = -1,x2 = 3 - 2m
AB = |x2 - x1| = |4-2m|
2m -3 = |4 - 2m|
(a) 3/2 < m < 2:
2m - 3 = 4 - 2m
m = 7/4
y = x^2 +3x/2 + 1/2
(b) m ≥ 2
2m -3 = 2m -4,不成立