In order to find the determinant we just multiply the diagonals
Then we substract the second result to the first:
[tex]\begin{gathered} \begin{bmatrix}{2} & {-1} & {} \\ {4} & {-5} & {} \\ & {} & {}\end{bmatrix}=2\cdot(-5)-4\cdot(-1) \\ =-10-\mleft(-4\mright)=-10+4 \\ =-6 \end{gathered}[/tex]
