Linear Algebra- Determinant

Let's try a 1x1 matrix.

If |a| = 3

What do we get if we multiply the first row by 2?

|2a| = 2|a| = 2(3) = 6

What do we get if we multiply the first colums by -1?

|-a| = -|a| = -(3) = -3

Are we getting anywhere?

You should have some Determinant Properties to help you with this.

If you continue to doubt, you can expand the Determinant by cofactors on the row or column of interest. This should convince you.
 
Thankkkkkkkkkkkk you the problem was that i trought the Jacobbi theorem was only for Rows and not columns
 
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