Plane & Spherical Trigonometry: A Tetrahedron Approach Dr. Millard R. Mamhot, Ph.D., Dr. Joemar C. Endam, Ph.D., Alice A. Mamhot, M.S., Emelyn C. Banagua, M.S., Jenette S. Bantug, M.S. ISBN: 978-971-9654-05-6