Wolfram Research
Wolfram Math World: Geometry
This MathWorld tutorial provides detailed overviews of the concepts and theorems associated with geometry. Most of the Math World sites are extensive and some require higher math knowledge to understand, links to terms and topics are...
Science and Mathematics Initiative for Learning Enhancement (SMILE)
Smile: Similarity
This site contains a lesson plan for high school age learners. The objective is to discover the factor of proportionality in similar polygons and to relate this factor to the perimeters and areas of similar polygons.
Rice University
Rice University: Cynthia Lanius: Golden Ratio
This site introduces students to the definition of golden ratio. It gives them a chance to estimate ratios and predict which figures are closest to the golden ratio. There is a link on this page that provides charts for students to...
Wolfram Research
Wolfram Math World: Geometric and Direct Similarity
This site contains a definition of the concept "directly similar." There are links to other defintions on this page. Great for reference.