x

a = 3 (slider from 0 to 10, step 0.001)
O: (0, 0)
B: (a, 0)
C: (a, a)
D: (0, a)
v1, a_1, b, c, d = Polygon(O, B, C, D)
A: (x(B), v1)
U: (x(B), (4 * x(B)))
Q: (x(B), 4 / x(B))