$\displaystyle \frac{2}{x-y}$\displaystyle \frac{2}{x-y}

$\displaystyle \frac{2}{x^2-y^2}$\displaystyle \frac{2}{x^2-y^2}

$\displaystyle \frac{2x}{x^2-y^2}$\displaystyle \frac{2x}{x^2-y^2}

$\displaystyle \frac{-2xy}{x+y}$\displaystyle \frac{-2xy}{x+y}