Summary: I love finding new and interesting proofs and demonstrations of geometric theorems particularly ones that are visual. One of my favorite theorems in coordinate geometry states that the area of the parallelogram $ABCD$ with vertices at $A(0,0)$, $B(a,b)$, $C(a+c,b+d)$ and $D(c,d)$ is equal to the product $ad-bc$. This editionâ€™s Column gives a nice visual demonstration, using Geometerâ€™s SketchPad, of this theorem when applied to any parallelogram, not just one with a vertex at the origin.