Date: Aug 20, 2012 9:22 AM Author: Peter Duveen Subject: Triangle similarity Books I have referenced mention various methods of proving triangle similarity. One of these is that, if two sides of a triangle are proportional to the corresponding sides of another triangle, and the included angles in each triange are equal, then the triangles are similar. It seems to me that if two sides of a triangle are proportional to corresponding sides of a second triangle, and a not-included angle is equal to the the corresponding not-included angle of the other triangle, then the triangles are similar also. But an examination of a few text books do not mention this as a theorem. In fact, one text has this as a problem, and says the triangles cannot be deemed similar in the second case. Any opinions out there?