x = -(2m+1)/ 2
y = [4(m^2-1)-(2m+1)^2] / 4 = (-4m -5) / 4
4x = -4m - 2 4y = -4m -5
4x - 4y = 3
所以顶点的轨迹方程:4x - 4y = 3