Dunham, William. Journey Through Genius. John Wiley & Sons, Inc. New York. 1990.
Heron's Formula and Brahmagupta's Generalization
Heron's Formula For Tetrahedrons
A Proof of the Pythagorean Theorem From Heron's Formula
Miscalculating Area and Angles of a Needle-like Triangle by William Kahan
Bill Casselman's Math 309