evaluate determinant?

Question

|3 0 |
|5 - 1 |

Answer 1

for a matrix, the determinate is the difference of the cross products
in the case of
|a b|
|c d|

the determinate is a*d - c*d

3*-1 - 5*0

-3

Answer 2

the answer is -3. You multiply (3)(-1) then subtract (5)(0).