Det [7, 2; 0, 3]

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 = 7 × 3 − 0 × 2.

Careful!

Always down minus up.

Up minus down gives the wrong sign.

2 Down minus up

7 times 3 is 21.

0 times 2 is 0.

21 minus 0 is 21.

So D = 21.

3 Check

Let's check the taking away by adding back: 21 + 0 = 21, the down product.

So D = 21 is right!

Let's look back.

First: multiply the diagonals.

Then: down minus up.

Last: check.