 \vec{ MA }. \vec{ MB } \; = \; MO² \; - \; R²  

R = 0.9 (slider from 0 to 2, step 0.1)
O = (-0.08772547663395171, 0.4194493201760195)
c = Circle(O, R)
M = (-1.3751445584540136, 0.11917664803139862)
C_1 = (1.1321322539535705, 0.08539597241512877)
a = Line(M, C_1)
A = Intersect(c, a, 1.0)
B = Intersect(c, a, 2.0)
b = OrthogonalLine(A, a)
C = Intersect(c, b, 2.0)
d = Segment(M, C)
e = Segment(C, B)