\(21\\ P=\dfrac{2}{x}-\dfrac{x^2y-\left(x^2-y^2\right)\left(x+y\right)-xy^2}{xy\left(x+y\right)}\cdot\dfrac{x+y}{x^2+xy+y^2}\\ P=\dfrac{2}{x}-\dfrac{x^2y-x^3-x^2y+xy^2+y^3-xy^2}{xy}\cdot\dfrac{1}{x^2+xy+y^2}\\ P=\dfrac{2}{x}+\dfrac{\left(x-y\right)\left(x^2+xy+y^2\right)}{xy}\cdot\dfrac{1}{x^2+xy+y^2}\\ P=\dfrac{2}{x}+\dfrac{x-y}{xy}=\dfrac{2y+x-y}{xy}=\dfrac{x+y}{xy}\)
\(22,\\ P=\dfrac{x^2-y\left(x-y\right)}{xy\left(x+y\right)}:\dfrac{y^2+x\left(x-y\right)}{x\left(x-y\right)\left(x+y\right)}:\dfrac{x}{y}\\ P=\dfrac{x^2-xy+y^2}{xy\left(x+y\right)}\cdot\dfrac{x\left(x-y\right)\left(x+y\right)}{y^2+x^2-xy}:\dfrac{x}{y}\\ P=\dfrac{x-y}{y}\cdot\dfrac{y}{x}=\dfrac{x-y}{x}\)
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