21\sqrt{2} 

21

\frac{21\sqrt{2}}{2} 

\frac{21\sqrt{2}}{2} 

A = (1, 3)
B = (4, 3)
C = (4, 1)
D = (1, 1)
poly1, a, b, c, d = Polygon(A, B, C, D)
I = Midpoint(c)
e = Segment(D, B)
f = Segment(A, I)
g = Segment(D, I)
h = Segment(I, C)
α = Angle(B, C, D)
β = Angle(C, D, A)
γ = Angle(D, A, B)
δ = Angle(A, B, C)