∠1 and ∠2 form a linear pair, so ∠1 and ∠2 are supplementary by the <u>LINEAR PAIR POSTULATE</u> . Therefore, m∠1 +<u>m∠2</u> = 180° by the definition of supplementary. It is given that ∠2 ≅ <u>∠3</u> so m∠2 = m∠3 by the <u>ANGLE CONGRUENCE POSTULATE</u> . By substitution, m∠1 + m∠3 = 180°, so ∠1 and ∠3 are supplementary by the definition of supplementary.
(I did it on a paper not to lose track.) First we go 25 north. Then ten east. Five south. And 10 west again. So in East/West we didn't move but we moved 5 down/south so we are still at twenty. If you don't understand still draw it on a paper.