# 3x3 Determinant

We can solve a 3x3 determinant by applying the following formula:

=

**a _{11}
a_{22}
a_{33} +
a_{12}
a_{23 }
a _{31} +
a_{13}
a_{21 }
a_{32} - **

**- a _{13}
a_{22}
a_{31} -
a_{12}
a_{21}
a_{ 33 } -
a_{11}
a_{23}
a_{32.}**

Since this formula is difficult to memorize, the rule of Sarrus is used to solve 3x3 determinants.

## Rule of Sarrus

The terms with a** + ****sign ** are formed by the elements of the **principal diagonal** and those of the **parallel diagonals** with its corresponding **opposite vertex**.

The terms with a** −**** sign ** are formed by the elements of the **secondary diagonal** and those of the **parallel diagonals** with its corresponding **opposite vertex**.