Bài 2:
Câu 3.
C = 2x + $xy^2$ - $x^2$ y - 2y tại x = $\dfrac{-1}{2}$ ; y = $\dfrac{-1}{3}$
C = 2 . $\dfrac{-1}{2}$ + $\dfrac{-1}{2}$ . ( $\dfrac{-1}{3}$ )^2 - ( $\dfrac{-1}{2}$ )^2 . $\dfrac{-1}{3}$ - 2 . $\dfrac{-1}{3}$
C = (-1) + $\dfrac{-1}{2}$ . $\dfrac{1}{9}$ - $\dfrac{1}{4}$ . $\dfrac{-1}{3}$ - $\dfrac{-2}{3}$
C = (-1) + $\dfrac{-1}{18}$ - $\dfrac{-1}{12}$ - $\dfrac{-2}{3}$
C = $\dfrac{-11}{36}$