Find the Determinant [[1,9],[1,5]]

$[\begin{array}{c} 1 & 9 \\ 1 & 5 \end{array}]$

Step 1

The determinant of a $2 \times 2$ matrix can be found using the formula $| \begin{array}{c} a & b \\ c & d \end{array} | = a d - c b$ .

$1 \cdot 5 - 1 \cdot 9$

Step 2

Simplify the determinant.

Simplify each term.

Multiply $5$ by $1$ .

$5 - 1 \cdot 9$

Multiply $- 1$ by $9$ .

$5 - 9$

Subtract $9$ from $5$ .

$- 4$