# Math Help - Matrix calculation/algebra!

1. ## Matrix calculation/algebra!

X is a 3x3 matrix (spaces used for separation)

1 3 9
1 4 16
1 5 25

I want to know X( X - 12I) where I is the 3x3 identity matrix. Can someone explain/show?

2. Originally Posted by acu04385
X is a 3x3 matrix (spaces used for separation)

1 3 9
1 4 16
1 5 25

I want to know X( X - 12I) where I is the 3x3 identity matrix. Can someone explain/show?
As it is written, it says multiple the identity matrix by 12, subtract X from the 12I and then multiple X by the that matrix.

$\begin{bmatrix}
1 & 3 & 9\\
1 & 4 & 16\\
1 & 5 & 25
\end{bmatrix}*\bigg(\begin{bmatrix}
1 & 3 & 9\\
1 & 4 & 16\\
1 & 5 & 25
\end{bmatrix}-\begin{bmatrix}
12 & 0 & 0\\
0 & 12 & 0\\
0 & 0 & 12
\end{bmatrix}\bigg)$

3. ## thanks!

Many thanks i was confusing myself with the relationship IA = AI = A