1. The problem statement, all variables and given/known data Determine the dimensions of the rectangle of largest area that can be inscribed in the right triangle shown? 2. Relevant equations AB/AD = BC/DE 3. The attempt at a solution I've been trying to do this problem. I looked online and saw an explanation without directly using the area of the triangle, found http://answers.yahoo.com/question/index?qid=20101128161728AA21pl7". Can someone remind me how to differentiate A = x H - (H/X)x^2 , in the last part of the problem? Is this from related rates?