Question

please help me quick Complete the proof of the exterior angle theorem. Given: ∠4 is an exterior angle of △ABC. Prove: m∠1+m∠2=m∠4

Answer 1

Explanation:

Statement Reason

1.∠4 is an exterior angle of ΔABC Given

2.∠3 and∠4 form a linear pair Linear pair theorem

3.∠3 is supplementary to ∠4 Property of supplementary angle

4.m∠3+m∠4=180° Definition of supplementary angle

5.m∠1+m∠2+m∠3=180° Triangle sum theorem

6.m∠1+m∠2+m∠3=m∠3+m∠4 From step 4 and 5

7.m∠1+m∠2=m∠4 Subtraction rule