Question

Answer 1

\(21+12\sqrt{3}=\left(3+2\sqrt{3}\right)^2\)

\(\Rightarrow\left\{{}\begin{matrix}a=3\\b=2\end{matrix}\right.\)

`@`\(3a+2b=3.3+2.2=13\)

`=>` Chọn B

Answer 2

\(21+12\sqrt{3}=21+2.6.\sqrt{3}=21+2.2\sqrt{3}.3=\left(2\sqrt{3}\right)^2+2.2\sqrt{3}.3+3^2=\left(3+2\sqrt{3}\right)^2\\ =>a=3;b=2\)

\(3a+2b=3.3+2.2=9+4=13\\ =>B\)