Question

Prove that the sum of the measures of the interior angles of a triangle is 180°. Be sure to create and name the appropriate geometric figures.

Answer 1

look at the picture showing triangle ABC



D || BC


so according to parallel lines theorem

angle 1 = angle B

angle 3 = angle C

angle 2 = angle A



1+2+3=180

then:

B+A+C=180

hope you understand it

good luck