This worksheet demonstrates a visual algorithm for calculating the greatest common divisor (GCD) of two positive integers. Start with a rectangle, and repeatedly remove the largest possible square from the top right corner, until the remaining shape is a square. The side length of the final square is the GCD of the side lengths of the original rectangle. This is a geometric interpretation of the Euclidean GCD algorithm.
An improved version of this worksheet was posted to the GeoGebra forum.