Question

prove that the sum of the angles of a triangle is 180

Answer 1

We know that,  alternate interior angles are of equal magnitude.

∠PAB + ∠BAC + ∠CAQ = 180°. where PQ line parallel to side BC touching vertex A.

∠PAB = ∠ABC & ∠CAQ = ∠ACB BECAUSE alternate interior angles are congruent..

Hence we get, ∠ABC + ∠BAC + ∠ACB = 180°   [Proved]

Answer 2

see this I'm sure you will understand