a = -13 (slider from -100 to 0, step 0.1)
b = 20 (slider from 0 to 40, step 10)
f = 20 (slider from -80 to 80, step 10)
F: (-f, 0)
F': (f, 0)
O = (0, 0)
A: (a, 0)
B: (a, b)
u = Vector(A, B)
c = Line(O, B)
d = Line(B, F)
C = Intersect(yAxis, d)
e = Line(C, xAxis)
B' = Intersect(c, e)
A': (x(B'), 0)
v = Vector(A', B')
G: (25 + a, 0)
g = Segment(B, G)
h = Segment(B', G)
θ = Angle(A, G, B)
θ' = Angle(A', G, B')
i = Line(F, F')
j = Line(O, C)