The part of the proof that uses the justification that angles with a combined degree of 90° are complementary is; Congruent Complements Theorem
How to prove complementary angles?
We are given;
m∠1 = 40°
m∠2 = 50°
∠2 is complementary to ∠3
We want to prove that ∠1 ≅ ∠3
Now, when the sum of two angles equals 90°, they are called complementary angles.
Now, looking at the angles, the proof that ∠1 ≅ ∠3 is Congruent Complements Theorem. This is because If two angles are complements of the same angle (or congruent angles), then the two angles are congruent.
Read more about Complementary angles at; https://brainly.com/question/98924
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