1. The problem statement, all variables and given/known data The electric power in Watts produced is given by p= 144r/(r+.8)^2 where r is the resistance in ohms. For what value of r is the power P a maximum? 2. Relevant equations 3. The attempt at a solution Using the quotient rule i found a derivative of.. dp/dt= 144(-r+.8) / (r + .8)^3 Now I need to set this equal to zero and solve for R? Multiplying the demonminator by 0 would leave me with just the numerator giving me.. -144r + 115.2 = 0 Solving for r gives me r = 0.8ohms Was there maybe a problem with my derivative?