The areas of two triangles which have an angle of the one equal to an angle of the other are to each other as the products of the sides including the equal angles. D c A' D' Hyp. In triangles ABC and A'B'C', ZA = ZA'. To prove AABC = ABxAC. A A'B'C' A'B'xA'C'... First Part of an Elementary Treatise on Spherical Trigonometry  Page 69 by Benjamin Peirce  1836  71 pages Full view 
