A Triangle's Angles

The sum of the measures of the interior angles of any triangle is 180°.

q \parallel r

B'

\angle B \cong \angle B'

C'

\angle C \cong \angle C'

m(\angle A) + m(\angle B') + m(\angle C') = 180°

Therefore

m(\angle A) + m(\angle B) + m(\angle C) = 180°

A = (0.18, 4.02)
B = (-1.3800000000000001, 1.44)
a = Segment(A, B)
C = (4.62, 1.46)
b = Segment(B, C)
c = Segment(C, A)
o = Line(B, A)
p = Line(C, A)
q = Line(B, C)
r = Line(A, q)