Area of semi-cirlce k and area of semi-circle d are equal which
is (3.14)*(b/2)^2/2 = 3.14*b^2/8 = A1.  'b' is divided by 2 to get the
radius of the whole cirlce of semi-circle k.  The area of the whole
cirlce is divided by 2 to get the area of the semi-circle k.   

Area of small semi-circle of each legs are equal to area of
large circle minus area of square divided by 4. It is divided by 4
because a square inscrbed by a circle gives 4 equal area
semi-circle.  That is,

Area of large circle = 3.14*(c/2)^2
Area of square        = a^2 = b^2

                 [3.14(c/2)^2 - b^2]/4 = 3.14c^2/16 - B^2/4 = A2

Area of moon = A1 - A2 = (3.14*b^2)/8 - (3.14*2*b)/16 +b^2/4 = b^4
Twice the area of moon = 2*(b/4) = (1/2)*b^2 = area of triangle

'b' and 'a' are the length of the two legs of the triangle which
are equal.  

A = (3.491405766816191, -0.7939735167565792)
B = (1.28066835194551, -0.7817594978898904)
A'_1 = Rotate(A, 90.0*°, B)
α = Angle(A, B, A'_1)
a = Segment(A'_1, B)
b = Segment(A, B)
c = Segment(A'_1, A)
d = Semicircle(A, B)
e = Semicircle(B, A'_1)
f = Semicircle(A'_1, A)
g = Segment(A'_1, B)
h = Segment(B, A)
i = Segment(A, A'_1)
poly2, a_1, b_1, a' = Polygon(B, A'_1, A)
Textpoly2: "Area " + (Name[B]) + (Name[A'_1]) + (Name[A]) + " = " + poly2
A'' = Mirror(A'_1, c)
A' = Mirror(A, c)
f' = Semicircle(A', A'')
D = Center(f)
q = CircleSector(D, A'', A)
s = CircleSector(D, A, A'')
areas = Area(s)
Texts: "Area of semicircle S= " + areas
C = Midpoint(a)
k = CircleSector(C, A'', B)
areak = Area(k)
j = Area(k)
areaq = Area(q)
l = Area(k)
text1: "Area of semicircle k= " + j