Consider the following function. f(x,y) = (x 4) 1n(x5y) (a) Find the critical point of f. If the critical point is (a, b) then enter 'a,b' (without the quotes) into the answer box. (b) Using your critical point in (a), nd the value of D(a, b) from the Second Partials test that is used to classify the critical point. (c) Use the Second Partials test to classify the critical point from (a). Enter your answer If the critical point is (a, I symbolically, as in these in then _ enter 'a,b' Into the examples answer box. Enter your answer symbolically, :I as in these exams Value or man)