1. The problem statement, all variables and given/known data 11. Maximize Q=xy, where x and y are positive numbers such that (4/3)x2 + y=16 2. Relevant equations 3. The attempt at a solution I know how to do it. The first time I did it. I multiplied the (4/3)x^2 +y=16 by (3/4) and got x^2+y=12 and then y=12-x^2 when solving for y. I used that equation to find the derivative of the product xy. How come I cannot do that because this still gave me a maximum and the critical point was still 2 but the other numbers were wrong. I don't understand why you can't solve for y like that?