n = -1.2 (slider from -10 to 30, step 0.01)
c: x^(2) + 2 * n * x * y + n * y^(2) + 2 * n * x + 2 * y + n + 1 = 0
a, b = Asymptote(c)
A: (-1, (-(n + 1)) / n)
B = Center(c)
u = Vector(((-(-1 + n + sqrt(1 - 2 * n + 5 * n^(2)))) / 2 * n, 1))