Geometry: Math Open Reference Site

Math Open Reference began as a project of a father who wanted to design an electronic, interactive textbook that would be better than the heavy textbooks his son carried. I'd say John Page has gone way beyond that goal. This site is awesome for students and teachers.


Euclidean Constructions

Since many schools are working on constructions, I'll highlight them. Once you look at the site, you will find it can be used for much more and in courses other than geometry.

This is a great site for Euclidean constructions, showing the compass and straightedge animations for those who need to rehearse and practice. Some may be completed in ways other than the methods you learned. Before using these in class, make sure you can prove why the method produces the desired result.

http://mathopenref.com/tocs/constructionstoc.html

http://www.mathopenref.com/constdividesegment.html

Common Core Geometry Standards

The site also includes the text of the Common Core Geometry Standards with text linked to appropriate pages in the Math Open Reference site. That is a great tool for teachers and students.

http://mathopenref.com/common-core.html

Using Math Open Reference Visuals

Need to explain why the SSA case is not enough to prove congruence? Look under standard G CO 8 for a link to an animation clearly showing the problem. This applies to a Geometry class, but the visual is also useful in an advanced class using trigonometry to solve triangles in the ambiguous case.

http://www.mathopenref.com/congruentssa.html

http://www.mathopenref.com/prism.html

How about being able to create and manipulate this figure to discuss cross section of a prism and height of an oblique prism. You can choose to allow oblique prisms or keep only right prisms.










Coordinate Geometry Methods

http://www.mathopenref.com/coordtriangleareabox.html

Coordinate geometry is something that many students find confusing. Looking at coordinate geometry methods, you can find the area of a triangle by finding the area of the bounding box, then subtracting the easy-to-find areas of the right triangles which are in the box, but outside the triangle.

You can manipulate the vertices to consider different triangles.








This site is great for student investigation or independent learning. Share it with your students, and take a look at how it can provide great teaching tools.

http://www.mathopenref.com/