Упрости выражения

a) \(\dfrac{x^{2}-y^{2}}{(x-y)^{2}}-\dfrac{x^{2}-y^{2}}{(x+y)^{2}}=\) [ ];

6. \(\dfrac{x^{2}-y^{2}}{2xy}:\left(\dfrac{1}{x}-\dfrac{1}{y}\right)=\) [ ].