a_1 = -1 (slider from -5 to 5, step 0.1)
A: (1, 5 + a_1)
B = (1, 1.0000000000000004)
D: (5 + a_1, 5 + a_1)
C: (5 + a_1, 1)
Flächeninhalt, a, b, c, d = Polygon(A, B, C, D)