Giải thích các bước giải:
Ta có:
\(\begin{array}{l}
a,\\
\dfrac{4}{{\sqrt 7 }} = \dfrac{{4\sqrt 7 }}{7}\\
b,\\
\sqrt {\dfrac{{{x^2}}}{5}} = \dfrac{{\sqrt {{x^2}} }}{{\sqrt 5 }} = \dfrac{{\left| x \right|}}{{\sqrt 5 }} = \dfrac{x}{{\sqrt 5 }} = \dfrac{{x\sqrt 5 }}{5}\,\,\,\,\,\,\,\,\,\,\left( {x \ge 0} \right)\\
c,\\
\dfrac{3}{{\sqrt x }} = \dfrac{{3\sqrt x }}{x}\\
d,\\
\dfrac{{\sqrt 5 - \sqrt 3 }}{{\sqrt 2 }} = \dfrac{{\sqrt 2 .\left( {\sqrt 5 - \sqrt 3 } \right)}}{2} = \dfrac{{\sqrt {10} - \sqrt 6 }}{2}\\
e,\\
\dfrac{{26}}{{5 - 2\sqrt 3 }} = \dfrac{{26.\left( {5 + 2\sqrt 3 } \right)}}{{\left( {5 - 2\sqrt 3 } \right)\left( {5 + 2\sqrt 3 } \right)}} = \dfrac{{26.\left( {5 + 2\sqrt 3 } \right)}}{{{5^2} - {{\left( {2\sqrt 3 } \right)}^2}}} = \dfrac{{26.\left( {5 + 2\sqrt 3 } \right)}}{{13}} = 2.\left( {5 + 2\sqrt 3 } \right)\\
f,\\
\dfrac{{9 - 2\sqrt 3 }}{{3\sqrt 6 - 2\sqrt 2 }} = \dfrac{{\sqrt 3 .\left( {3\sqrt 3 - 2} \right)}}{{\sqrt 2 .\left( {3\sqrt 3 - 2} \right)}} = \dfrac{{\sqrt 3 }}{{\sqrt 2 }} = \dfrac{{\sqrt 6 }}{2}
\end{array}\)
