See how many pieces of information you can observe. You should be
able to prove that the two shaded rectangles have the same area.

a = 1.75 (slider from 0.01 to 4.99, step 0.01)
m = -0.5 (slider from -1 to -0.5, step 0.01)
A = (0, 10)
B = (0, 0)
b = Segment((0.0, 0.0), (0.0, 10.0))
C: (-(10.0) / m, 0.0)
c = Segment(A, C)
D: (0.0, 10.0 - a)
E: (-(10.0 - a) / m, a)
F: (-(10.0 - a) / m, 0.0)
d = Segment(E, F)
G: (0.0, a)
e = OrthogonalLine(D, b)
H = Intersect(e, c)
f = Segment(D, H)
g = OrthogonalLine(H, xAxis)
I = Intersect(g, xAxis)
h = Segment(G, E)
i = Segment(H, I)
J = Intersect(h, i)
poly1, d_1, h_1, j, g_1 = Polygon(D, H, J, G)
poly2, j_1, e_1, f_1, i_1 = Polygon(J, E, F, I)
k = Segment(B, C)
l = Segment(A, D)
n = Segment(E, F)