(căn 10 – căn 6) . căn tất cả của 4 + căn 15

\(\begin{array}{l}
\left( {\sqrt {10} – \sqrt 6 } \right).\sqrt {4 + \sqrt {15} } \\
= \left( {\sqrt 2 .\sqrt 5 – \sqrt 2 .\sqrt 3 } \right).\sqrt {4 + \sqrt {15} } \\
= \sqrt 2 \left( {\sqrt 5 – \sqrt 3 } \right).\sqrt {4 + \sqrt {15} } \\
= \left( {\sqrt 5 – \sqrt 3 } \right).\sqrt {2.\left( {4 + \sqrt {15} } \right)} \\
= \left( {\sqrt 5 – \sqrt 3 } \right).\sqrt {8 + 2\sqrt {15} } \\
= \left( {\sqrt 5 – \sqrt 3 } \right).\sqrt {5 + 2\sqrt 5 .\sqrt 3 + 3} \\
= \left( {\sqrt 5 – \sqrt 3 } \right).\sqrt {{{\left( {\sqrt 5 + \sqrt 3 } \right)}^2}} \\
= \left( {\sqrt 5 – \sqrt 3 } \right)\left( {\sqrt 5 + \sqrt 3 } \right)\\
= 5 – 3 = 2
\end{array}\)