Ta có
$x^2 - xy = x(x-y); y^2 - xy = y(y-x) = -y(x-y); x^2 - y^2 = (x-y)(x+y)$
Vậy mẫu thức chung là $xy(x-y)(x+y) = xy(x^2-y^2)$
Khi đó ta có
$\dfrac{2}{x^2-xy} = \dfrac{2y(x+y)}{xy(x-y)(x+y)} = \dfrac{2y^2 + 2xy}{xy(x^2-y^2)}$
$\dfrac{x}{y^2-xy} = \dfrac{-x}{y(x-y)} = \dfrac{-x.x(x+y)}{xy(x-y)(x+y)} = \dfrac{-x^3 - x^2y}{xy(x^2-y^2)}$
$\dfrac{x+3}{x^2-y^2} = \dfrac{xy(x+3)}{xy(x-y)(x+y)} = \dfrac{x^2y + 3xy}{xy(x^2 - y^2)}$
