Math Open Reference is a free interactive math reference covering high school geometry, functions, and calculus. Five organizing topics cover plane, coordinate, and solid geometry, plus trigonometry and calculus. Four function explorers and a general online scientific calculator arm kids with awesome tools that really help them visualize what all these numbers and formulas actually mean.
Most entries open with a definition, follow with concise explanations of relevant concepts, then end with links to other relevant topics. Embedded "Try This" activities invite kids to interact with dynamic diagrams by moving intersecting points, lines, or vertices and watching the results. Sections within entries do not follow a formula but are appropriate to the topic: For central angle theorem, it's simply "Exception." About 40 entries are actually constructions -- step-by-step animations showing kids exactly how to find the "center of a circle using any right-handed object," for example.
Math Open Reference truly shines despite its plain package and often confusing sidebar ads for other math sites. Concise, accurate explanations provide a solid foundation for a series of dynamic construction and manipulation applets that pull kids into the experience and build deeper, concrete understanding of geometry concepts. The constructions in particular show kids through animated protractors and pencils (and downloadable worksheets) how to bisect an angle, divide a line segment into equal parts, or draw a parallel line through a point.
While site owner John Page calls it a textbook in his mission statement, the terms reference and construction guide are more precise. There are no assessments or exercises for the definitions, nor standards alignment, but the construction tools and worksheets are homework for this portion of the curriculum. Content is offered in 72 languages through Google translate, including Esperanto, Haitian Creole, and Basque. Wow! Math Open Reference puts quality information and protractors in kids' hands in class, at home, or anytime.
Three articles linked to the About page communicate the site owner's thinking on pedagogy, technology in education, and how Math Open Reference can be used in the classroom. Testimonials concisely describe how you can easily project and step through the constructions with the whole class. Next, students re-create them using the site until they are eventually able to do it unaided with real drawing tools. Of course, when homework time rolls around, kids can peek back at the site if memory fails. Function explorers provide concrete illustrations of linear equations and more, and could be taught using a similar process. Definitions and explanations could be used to introduce concepts and serve as a basis for simple quizzes.
According to the owner, Math Open Reference outshines Geometer's Sketchpad software for three reasons: It draws portions of circles (arcs) needed for constructions, it is freely accessible at home, and animations include images of the drawing instruments.