Rút gọn biểu thức (P = {left( {{x^{frac{1}{2}}} - {y^{frac{1}{2}}}} ight)^2}{left( {1 - 2sqrt {frac{y}{x}} + frac{y}{x}} ight)^{ - 1}}?)

\(P = {\left( {{x^{\frac{1}{2}}} - {y^{\frac{1}{2}}}} \right)^2}{\left( {1 - 2\sqrt {\frac{y}{x}}  + \frac{y}{x}} \right)^{ - 1}} = {\left( {\sqrt x  - \sqrt y } \right)^2}{\left( {1 - \sqrt {\frac{y}{x}} } \right)^{ - 2}} = \frac{{{{\left( {\sqrt x  - \sqrt y } \right)}^2}}}{{{{\left( {\frac{{\sqrt x  - \sqrt y }}{{\sqrt x }}} \right)}^2}}} = x.\)