Wyznacznik $\left[\begin{array}{cc}1 & 2\\4 & 5\end{array}\right]$

Oblicz $\left|\begin{array}{cc}1 & 2\\4 & 5\end{array}\right|$.

Wyznacznikiem macierzy 2x2 jest $\left|\begin{array}{cc}a & b\\c & d\end{array}\right| = a d - b c$.

$\left|\begin{array}{cc}1 & 2\\4 & 5\end{array}\right| = \left(1\right)\cdot \left(5\right) - \left(2\right)\cdot \left(4\right) = -3$

$\left|\begin{array}{cc}1 & 2\\4 & 5\end{array}\right| = -3$A