1.  http://www.math.com/school/subject3/lessons/S3U3L4GL.html

2.  http://mathworld.wolfram.com/PythagoreanTheorem.html

3.  http://www.themathlab.com/Algebra/lines%20and%20distances/pythagor.htm

4.  http://www.historyforkids.org/learn/greeks/science/math/pythagoras.htm

5.  http://www.pbs.org/teachersource/mathline/concepts/historyandmathematics/activity1.shtm