2 câu trả lời
$\begin{array}{l}
3\sqrt {12} - 4\sqrt 3 + 5\sqrt {27} \\
= 3.\sqrt {{2^2}.3} - 4\sqrt 3 + 5.\sqrt {{3^2}.3} \\
= 3.2\sqrt 3 - 4\sqrt 3 + 5.3\sqrt 3 \\
= 6\sqrt 3 - 4\sqrt 3 + 15\sqrt 3 \\
= 13\sqrt 3 \\
\end{array}$
(3$\sqrt{12}$ `- 4`$\sqrt{3}$ `+` $\sqrt{15}$)$\sqrt{3}$ `- 2`$\sqrt{5}$
`=` (6$\sqrt{3}$ `-` 4$\sqrt{3}$ `+` $\sqrt{15}$)$\sqrt{3}$ `- 2`$\sqrt{5}$
`=` (2$\sqrt{3}$ `+` $\sqrt{15}$)$\sqrt{3}$ `- 2`$\sqrt{5}$
`= 6 + 3`$\sqrt{5}$ `- 2`$\sqrt{5}$
`= 6 +` $\sqrt{5}$
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