Category Archives: Math Software

Soccer Challenges: Angling for a Shot on Goal

With the World Cup in our hemisphere, and the US squad having started out with a win over Ghana, my thoughts turned to the mathematics of soccer. My friend Henri Picciotto has a nice page about the shooting angle, the angle within which a shot is on goal, so I thought of … Continue Reading ››

Questioning Some Dynamic Geometry Angle Wisdom

For the past eight months, my colleague Scott Steketee and I have collaborated with the authors of the elementary curriculum Everyday Mathematics to design interactive Web Sketchpad models for their next edition. When it came time to create a Sketchpad representation of an isosceles triangle, I built the interactive triangle model below. Try … Continue Reading ››

Unlocking the Patterns of Multiples and Factors

In several of my earlier blog posts, I've written about Sketchpad activities that present factors and multiples in puzzle form (see, for example, When Factoring Gets Personal). Now I'd like to introduce you to another puzzle of mine called Open the Safe that also focuses on factors and multiples. Below … Continue Reading ››

A Funhouse Mirror of Sketchpad Transformations

Did you know that The Geometer's Sketchpad is a great tool for creating funhouse mirror pictures? Sure, Sketchpad can reflect, rotate, translate, or dilate a picture, but these operations are rather tame: They transform images uniformly, producing pictures that are easily recognizable versions of the original. By contrast, Sketchpad's "custom transform" feature allows you to apply non-linear transformations … Continue Reading ››

Surprise, Surprise: Tangent Circles Produce an Ellipse

This will be the first in an occasional series of posts that offer interactive Web Sketchpad models for drawing conic sections. My interest in conic sections dates back to the mid 1990s, when I authored Exploring Conic Sections with The Geometer's Sketchpad for Key Curriculum Press . You can read more about it in … Continue Reading ››

Iteration in the Complex Plane

The cover story of the April 2014 issue of Mathematics Teacher is on "Iteration in the Complex Plane", by Robin S. O'Dell. It sounds like pretty advanced mathematics, but is surprisingly accessible with The Geometer's Sketchpad. It's all based on the surprising principle that you can multiply two complex numbers very easily if … Continue Reading ››