I need help with this problem... How do I actually prove this? With a diagram or an explanation? A quadrilateral has vertices A = (0, 0), B = (1, 3), C = (0, 4), and D = (−1, 1). Prove that ABCD is a parallelogram.

I would draw this on a graph and then prove that the quadrilateral is a parallelogram by using slopes.

The slope of AB equals the slope of CD and the slope of AD equals the slope of BC; therefore,

since the opposite sides are parallel, this is a parallelogram.