f(x) = x^(2)
a = -0.8 (slider from -5 to 5)
b = 2.8 (slider from -5 to 5)
A: (a, f(a))
B: (b, f(b))
g = Line(A, B)
A': (a, 0)
B': (b, 0)
I = Midpoint(A', B')
H: (x(I), f(x(I)))
h = Segment(I, H)
i = Segment(A, A')
j = Segment(B, B')
k = Line(H, g)