posted by EKH .
quadrilateral A B C D on a graph. Point A is at ( -5, -1), Point B is at ( 6, 1), Point C is at (4, -3), Point D is at (-7, -5).
Prove the quadrilateral is a parallelogram by using Theorem 5-8; if one pair of opposite sides of a quadrilateral is both congruent and parallel, then it is a parallelogram.
figure the length and slope of AB and CD. If they match, it's a ||-ogram.