Developing Proof Complete this paragraph proof of Theorem 3-6. If two lines and a transversal form supplementary same-side interior angles, then the two lines are parallel. Given: 21 and 22 are supplementary. C Prove: € || m Proof: 22 is a supplement of a. *? and 23 is a supplement of b. ?.Since supplements of the same angle are congruent, c. ? = d.? , Since 22 and 23 are also corresponding angles, é || m by the e. ? Postulate. 3 2 6.