In how many different ways can you build a rhombus that stays a rhombus when its vertices are dragged? This assignment, a mainstay of Sketchpad workshops, invariably leads to great discussions because there are a multitude of ways to construct a rhombus, with each method highlighting different mathematical properties of the quadrilateral.

# Tag Archives: Web Sketchpad

# A Trio of Parabola Constructions

In my prior blog posts, I've presented methods for constructing ellipses using Web Sketchpad and paper folding. The other conic sections are feeling a bit left out, so let's explore some techniques for constructing parabolas.

All three Web Sketchpad models below (and here) are based on the distance definition of a parabola: The set … Continue Reading ››

# An Interactive Approach to Finding nth Roots

When students find the nth roots of a complex number, they use de Moivre's Theorem and a fair bit of calculation and trigonometry. In this blog post, I'm going to approach the topic from a more visual perspective and make use of the following geometric way to think about complex number multiplication: To multiply two complex … Continue Reading ››

# Beam of Light

This month's post is based on a problem that appears in Martin Gardner's *Sixth Book of Mathematical Diversions from Scientific American*. Below (and here) is a Web Sketchpad model of an orderly forest. There is a tree at every point whose *x*- and *y*-coordinates are both integers. These are the green points. … Continue Reading ››

# Catching Up with New Web Sketchpad Functionality

This past January, we introduced the Web Sketchpad Tool Library and Viewer. The Tool Library is a collection of over 60 mathematical tools for customizing a Web Sketchpad model, making it possible for teachers to decide which tools students have available to them on an activity-by-activity basis. The Viewer is a site … Continue Reading ››

# The Folded Circle Construction

Of all the conic section construction techniques, my favorite is undoubtedly the approach that requires nothing more than a paper circle.

Here's what to do: Draw or print a circle and its center, point *A,* on a sheet of paper. Cut out the circle. Mark a random point *B* anywhere on the circle. Then, fold … Continue Reading ››

# Dividing and Subdividing

Given a strip of paper, how might you divide it into fourths without using a ruler? Undoubtedly, you'd fold the strip in half and then in half again to locate the quarter marks. Now suppose that your goal is to divide a strip into sixths. You might start by folding the strip into thirds and … Continue Reading ››

# Circle Tracer Challenges

Geometry tends not to receive much love in elementary curricula, and that's a shame. In this post, I'll describe some of my new ideas for using Web Sketchpad to introduce young learners to fundamental properties of circles.

On page 1 of the websketch below (and here), begin by asking students to drag … Continue Reading ››

# What’s New with Web Sketchpad in 2019

For the past five years, Scott and I have featured interactive Web Sketchpad models in nearly all our Sine of the Times blog posts. As much fun as it's been to build "websketches" to share with you, we've really wanted to put the creative power of Web Sketchpad into your hands.

And now, finally, that's … Continue Reading ››

# Multiplication Is Not Repeated Addition

On the NCTM discussion site myNCTM, there's currently an extended discussion about "Division and multiplication of fractions." As the discussion has continued, I've grown concerned with what I see as a fundamental problem with the way we often introduce multiplication as repeated addition: "Multiplying 4 by 5 means we're combining five groups of four items. … Continue Reading ››