Learn to use the Pythagorean Theorem with non-right triangles. Pupils use the interactive to discover the relationship between the lengths of sides for acute and obtuse triangles. They compare the squares of the sides of the triangles to...

Stuck with triangle proofs? Take a 180° and provide learners with a guided activity that tests their knowledge with triangle inequalities. The questions require different types of proofs that range in levels of difficulty. 

This tutorial discusses triangle inequality and provides practice problems for students to try out their skills. The teacher resource page contains a lesson plan for a yummy activity involving licorice.

This site has a description of the triangle inequality theorem along with a visual representation, and animation explaining the triangle inequality rule with the radii of circles at the segment endpoints. Links to related terms, more...

Given examples of triangles and their component parts, the student will use explorations and concrete models to verify and apply the and find the sum of interior angles.

A complete reference guide to types of triangles and triangle perimeter and area. It provides definitions and interactive animated activities that enhance further explanation.

Given the lengths of two sides of a triangle, what can we say about the third side? Students receive immediate feedback and have the opportunity to try questions repeatedly, watch a video or receive hints.