P \; : \;  \; y \; = \;  \frac{ 1 }{4 }  \; x^2

k = -2.8 (slider from -10 to 10, step 0.1)
M: (k, 0.25 k^(2))
T, b = Tangent(M, P)
N = OrthogonalLine(M, T)
a = Line(M, yAxis)
c = Mirror(a, N)
A_1 = Point(a)
d = Ray(M, A_1)
B_1 = Point(c)
R = Ray(M, B_1)
C = Intersect(P, R, 2)
e = Segment(M, C)
B = Intersect(N, yAxis)
A = Intersect(T, yAxis)
F = Midpoint(B, A)
D = Point(P)

Tool: Rayon Incident (command RayonIncident)
Input: c, M, I
Output: b, R

b, d = Tangent(M, c)
e = OrthogonalLine(M, b)
R = Mirror(I, e)