Question

Quadrilateral ABCD has vertices A(1, 0) B(5, 0) C (7, 2) D(3, 2). Use slope to prove that ABCD is a parallelogram.

Answer 1

If ABCD is a parallelogram, we have to prove that slope of AB = CD and slope of BC = DA. Using the formula m = (y1-y2) / (x1-x2), the slope of line segment AB = 0/-4,  CD = 0/-4, BC = 1, DA  = 1. Going back to the condition, the slope we get for each line segment proves that ABCD is a parallelogram.