8.
\((1)\)计算\((\dfrac{2}{{{a}^{2}}-{{b}^{2}}}-\dfrac{1}{{{a}^{2}}-ab})\div \dfrac{a}{a+b}=\)________
\((2)\)计算:\(\dfrac{{{a}^{2}}}{a-b}-\dfrac{{{b}^{2}}}{a-b}=\)________.
\((3)\)化简:\(\dfrac{{{(a+b)}^{2}}}{{{a}^{2}}+{{b}^{2}}}-\dfrac{2ab}{{{a}^{2}}+{{b}^{2}}}=\)________.
\((4)\)化简:\((\dfrac{2x-1}{x+1}-x+1)\div \dfrac{x-2}{{{x}^{2}}+2x+1}=\)________.