matrix to the power

**BadMonkey** · November 14th 2010, 09:47 AM

Hi, matrix A=
-7 18
-3 8

I need to find $A^2$ using $A^2=(P)(D^2)(P^-1)$
P=
2 3
1 1

P^-1 =
-1 3
1 -2

D^2 =
4 0
0 1

My problem is how do I multiply out PD^2P^-1 correctly? its doesnt seem to give A^2 as the answer?

Thanks

**FernandoRevilla** · November 14th 2010, 11:48 AM

Originally Posted by BadMonkey

Hi, matrix A=
My problem is how do I multiply out PD^2P^-1 correctly? its doesnt seem to give A^2 as the answer?

Let us see. Perhaps the origin of the problem is:

(i) The eigen values of $A$ are $\lambda_1=2,\;\lambda_2=-1$ (both simple), so $A$ is diagonalizable, being:

$D=\begin{bmatrix}{2}&{0}\\{0}&{-1}\end{bmatrix}$

(ii) In fact, the $P$ matrix satisfies:

$P^{-1}AP=D$ or equivalently $A=PDP^{-1}$

(iii) Then,

$A^2=PDP^{-1}PDP^{-1}=PD^2P^{-1}$ .

(iv) So,

$A^2=\begin{bmatrix}{2}&{3}\\{1}&{1}\end{bmatrix}\b egin{bmatrix}{4}&{0}\\{0}&{1}\end{bmatrix}\begin{b matrix}{-1}&{3}\\{1}&{-2}\end{bmatrix}=\ldots=\begin{bmatrix}{-5}&{18}\\{-3}&{10}\end{bmatrix}$

Now, find $A^2$ directly. You'll obtain the same matrix.

Regards.

Thread: matrix to the power

LinkBack

Thread Tools

Display

matrix to the power

Similar Math Help Forum Discussions

Power of a Matrix

Matrix to the Power 10

Power of a matrix

Raising a Matrix to a power, help please!

Matrix Power

Search Tags