This is not a general mathematics help site. In the future, please send mathematics questions to places set up to handle them.
The http://mathworld.wolfram.com/ web pages have a Contact the MathWorld Team link, usually at the bottom of the page.
The reference in the web page you listed,
Rhoad, R.; Milauskas, G.; and Whipple, R., Geometry for Enjoyment and Challenge, rev. ed. Evanston, IL: McDougal, Littell & Company, 1984,
or similar geometry text, is probably available in a library.