Question

Use triangle ABC below to answer the question that follows:

Answer 1

That would be (1) A+B=180-C. It's true but not useful for the proof.

Answer 2

Answer: Choice 1) The sum of the angles A and B are supplementary to angle C

Why is this the answer? Because we'll use facts 2 through 4 to help prove the triangles similar. If fact 2 is true, then fact 3 leads to helping set up the congruent corresponding angles (either A = D or C = E). Fact 4 is true because all angles are congruent to themselves, and this fact is the other angle pair we need to prove the triangles similar.

We don't use fact 1 even though it's a true statement. The fact that A+B+C = 180 isn't really useful to compare across two triangles.