$\frac{x+y}{\frac{1}{x}+\frac{1}{y}} = $

$\frac{-x^{2}}{x^{2}-9}+\frac{x}{x+3} = $

$\frac{x^{3}+8}{(x+2)^{2}}-\frac{x+4}{x+2} = $

$(\frac{1}{x^{2}}-\frac{1}{y^{2}})\div(\frac{1}{x}+\frac{1}{y}) = $

$\frac{\frac{3}{x}+3}{\frac{5}{x^{2}}-\frac{1}{x}} = $

$\frac{\frac{1}{a}-\frac{1}{b}}{\frac{1}{a}+\frac{1}{b}} = $

$\frac{1}{x+2}-\frac{2x}{x^{2}-x-2} = $