Cho K = {left( {{x^{frac{1}{2}}} - {y^{frac{1}{2}}}} ight)^2}{left( {1 - 2sqrt {frac{y}{x}} + frac{y}{x}} ight)^{ - 1}}

* Hướng dẫn giải

\(\begin{array}{l}
K = {({x^{\frac{1}{2}}} - {y^{\frac{1}{2}}})^2}{(1 - 2\sqrt {\frac{y}{x}}  + \frac{y}{x})^{ - 1}}\\
 = (x + y - 2\sqrt {xy} ).\frac{1}{{1 - 2\sqrt {\frac{y}{x}}  + \frac{y}{x}}}\\
 = x(x + y - 2\sqrt {xy} ).\frac{1}{{x - 2\sqrt {xy}  + y}} = x.
\end{array}\)