## Algebra: A Combined Approach (4th Edition)

The slope between $(1,3)$ and $(2,1)$ $\frac{1-3}{2-1}=\frac{-2}{1}=-2$ The slope between $(-4,0)$ and $(-3,-2)$ $\frac{-2-0}{-3-(-4)}=\frac{-2}{1}=-2$ Two sides have the same slope, so these two sides are parallel. These sides are also opposite sides. So this is a parallelogram.