Let $f ( x , y ) = a x ^ { 2 } - 2 a x y + 2 y ^ { 2 } - b x$

Essay

Let $f ( x , y ) = a x ^ { 2 } - 2 a x y + 2 y ^ { 2 } - b x$ , where a, b are any numbers with a $\neq$ 2.
Find the critical point of f.(Express your answer in terms of the constants a and b.)