Geometric View Connecting Determinants and Area

Editors Note:
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 edition's Column gives a nice visual demonstration, using Geometer's SketchPad, of this theorem when applied to any parallelogram, not just one with a vertex at the origin.
Jon Choate