# What is the cofactor expansion method to finding the determinant?

##### 1 Answer

Hello !

Let

Choose a column : the column number

The **cofactor expansion formula** (or Laplace's formula) for the

where

Note that the number **cofactor** of place

Maybe it looks like complicated, but it's easy to understand with an example. We want calculate

If we develop on the 2nd column, you get

so :

Finally,

To be efficient, you have to choose a line which has a lot of zeros : the sum will be very simple to calculate !

**Remark**. Because

where