Answer:
Step-by-step 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
