[tex] \large \boxed{ \begin{array}{l} \begin{bmatrix} 1& - 4 \\ 3&9\end{bmatrix} \\ \\ \rm \: det = 1 \times 9 - ( - 4) \times 3 \\ \\ \rm \: det = 9 + 4 \times 3 \\ \\ \rm \: det = 9 + 12 \\ \\ \boxed{ \boxed{ \rm{det = 21}}} \leftarrow \textsf{Verdadeiro}\end{array}}[/tex]
