I know this block by the name MARYS' TRIANGLE. Here's a link for the math:
http://phoenixquiltguild.org/meeting...sTriangle.html
Also, from Sally Schneider - the Queen of Marys' Triangles, has this information:
http://www.sallyschneider.com/supply...206%20hour.pdf
Also known as Shaded Four Patch.
Hope it helps!
Jane