In what directions is the derivative of f(x,y)= xy + y2 at P(8,5) equal to zero? Select the correct choice below and, if necessary, fill in the answer box to complete your choice. А. 5 18 5 18 u =...

Extracted text: In what directions is the derivative of f(x,y)= xy + y2 at P(8,5) equal to zero? Select the correct choice below and, if necessary, fill in the answer box to complete your choice. А. 5 18 5 18 u = V349" V349" V349 (Simplify your answer. Use a comma to separate answers as needed. Type your answer in terms of i and j.) V349 B. There is no solution.