Đáp án:
A=-1
Giải thích các bước giải:
\(\begin{array}{l}
A = \left[ {\dfrac{{\sqrt y }}{{\sqrt x \left( {\sqrt x - \sqrt y } \right)}} + \dfrac{{\sqrt x }}{{\sqrt y \left( {\sqrt y - \sqrt x } \right)}}} \right].\dfrac{{\sqrt {xy} }}{{\sqrt x + \sqrt y }}\\
= \left[ {\dfrac{{\sqrt y }}{{\sqrt x \left( {\sqrt x - \sqrt y } \right)}} - \dfrac{{\sqrt x }}{{\sqrt y \left( {\sqrt x - \sqrt y } \right)}}} \right].\dfrac{{\sqrt {xy} }}{{\sqrt x + \sqrt y }}\\
= \left[ {\dfrac{{y - x}}{{\sqrt {xy} \left( {\sqrt x - \sqrt y } \right)}}} \right].\dfrac{{\sqrt {xy} }}{{\sqrt x + \sqrt y }}\\
= \dfrac{{y - x}}{{\left( {\sqrt x - \sqrt y } \right)\left( {\sqrt x + \sqrt y } \right)}}\\
= \dfrac{{ - \left( {x - y} \right)}}{{x - y}} = - 1
\end{array}\)
