1. The problem statement, all variables and given/known data I'm stuck on part b) of the question, but this includes the whole thing: A farmer wants to make a rectangular paddock with an area of 4000m^2. However, fencing costs are high and she wants the paddock to have a minimum perimeter. a) Show that the perimeter is given by the equation P = 2x + 8000/x b) Find the dimensions of the rectangle that will give the minimum perimeter, correct to 1 decimal place. 3. The attempt at a solution a) A = 4000 = xy y = 4000/x P = 2x + 2y = 2x + 2(4000/x) = 2x + 8000/x Okay, so that was easy. b) I assume here I just find the first derivative of P (to find minima) dP/dx = 2 + 8000/x^2 So; 8000/x^2 + 2 = 0 Obviously this won't solve because I can't find x ( negative sq. root)... Where have I gone wrong exactly?