Cynthia is writing a proof of the theorem stated below.

Theorem: The sum of interior angles of a triangle is 180°.

She first drew the figure shown below.

Which theorem will she most likely use in the proof?

Question

Cynthia is writing a proof of the theorem stated below.
 
Theorem: The sum of interior angles of a triangle is 180°. 

She first drew the figure shown below.
 

 
Which theorem will she most likely use in the proof?

anonymous · Answer

Vertical angles are congruent.

 Alternate Interior Angles formed by parallel lines and their transversal are complementary.

 If two angles form a straight angle, then they are supplementary.

 Corresponding angles formed by parallel lines and their transversal are supplementary.