In a word processing document or on a separate piece of paper, use the guide to construct a two column proof proving that lines l and m are parallel. angles 1 and 2 are supplementary by definition. submit the entire proof to your instructor. given: ∠1 and ∠2 are supplementary angles prove: l || m statement                                                   reason  1.∠1 and ∠2 are supplementary angles           1. given  2. m∠1 + m∠2 = 180°                                       2.  3. ∠1 and ∠3 are supplementary angles           3. exterior sides in opposite rays  4.                                                                       4.  5. m∠1 + m∠2 = m∠1 + m∠3                           5.6.                                                                       6.  7. l || m                                                             7.