Author: Benny Varghese  PGT Maths

Drag D to be interior to / on /exterior to the circle 
When <C=<D then observe that D is also on 
the circle....so that 4 points are concyclic...
 

Drag A or B or C to get various cases...

Prepared by :
Benny Varghese
PGT Mathematics
JNV Pathanamthitta

a BENTECH presentation.......
4  concyclic points.....A B C D

Drag_Me = 3.4 (slider from 0.5 to 5, step 0.1)
A_1 = (6.8420000000000005, -0.5680000000000012)
c = Circle(A_1, Drag_Me)
B_1 = Point(c)
B = Point(c)
A = Point(c)
t = Segment(B, A)
f = OrthogonalLine(A_1, t)
H = Point(c)
a = Line(H, A_1)
C = Point(c)
b = Segment(C, A)
d = Segment(C, B)
β = Angle(A, C, B)
D = (9.636000000000001, 4.821999999999999)
e = Segment(A, D)
g = Segment(D, B)
γ = Angle(A, D, B)