1. The problem statement, all variables and given/known data there's a picture of the question... from my text book http://photos-h.ak.fbcdn.net/hphotos..._1385551_n.jpg [Broken] thers a diagram image of the problem too to help understand 2. Relevant equations well its a word problem, i used cosine rule at beginining and then pythagoras...i dont know what to do next but i think you calculare the area and then derivative. but i dont know how (whats the equation for the area) 3. The attempt at a solution well i used the cosine rule for triangle BCO BC^2 = 10^2 + 10^2 - 2x10x10 cosθ BC = √(200-200cosθ) XY = BC BY^2 = BX^2 + XY^2 = 400 = BX^2 + (200-200cosθ) BX^2 = 200 + 200cosθ BX = √(200+200cosθ) now what do i do? reply asap ! :P thankss !!