matrix

$\begin{bmatrix} 1 && 2 \\ 3 && 4 \end{bmatrix}$

LaTeX code: (\begin{bmatrix}1 && 2  

                     3 && 4 \end{bmatrix}) without the ()

In calculator, Matrices can't be calculated but value of the above one (the 1 2 3 4 one) = 2 x 3 - 1 x 4.