t = 1 (slider from -5 to 5, step 0.1)
h = -0.6 (slider from -5 to 5, step 0.01)
a: t / 2 * x - t^(2) / 4 - y = 0
d: (t + h) / 2 * x - (t + h)^(2) / 4 - y = 0
A = Intersect(c, a)
B = Intersect(c, d)
C = Intersect(a, d)