Det [4, 2; 3, 1]

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 = 4 × 1 − 3 × 2.

Careful!

Always down minus up.

Up minus down gives the wrong sign.

2 Down minus up

4 times 1 is 4.

3 times 2 is 6.

4 minus 6 is −2.

So D = −2.

3 Check

Let's check the taking away by adding back: −2 + 6 = 4, the down product.

So D = −2 is right!

Let's look back.

First: multiply the diagonals.

Then: down minus up.

Last: check.