Det [5, 2; 3, 4]

Step by step

The question

Question: find the determinant of this matrix.

The determinant is one number we get from a square matrix.

We write the matrix between two straight lines, and call it D.

1 Multiply the diagonals

So D = 5 × 4 − 3 × 2.

Careful!

Always down minus up.

Up minus down gives the wrong sign.

2 Down minus up

5 times 4 is 20.

3 times 2 is 6.

20 minus 6 is 14.

So D = 14.

3 Check

Let's check the taking away by adding back: 14 + 6 = 20, the down product.

So D = 14 is right!

Let's look back.

First: multiply the diagonals.

Then: down minus up.

Last: check.