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If $A=\begin{bmatrix} 2 & 4 \\ 0 & 3 \end{bmatrix}$ then find the eigen values of $6A^{-1}+A^3+2I$
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written 5.0 years ago by | • modified 5.0 years ago |
Solution:
$A=\begin{bmatrix} 2 & 4 \\ 0 & 3 \end{bmatrix}$
The characteristic equation is $|A-\lambda I| = 0$
$A=\left |\begin{matrix} 2-\lambda & 4 \\ 0 & 3-\lambda \end{matrix} \right|$=0
$(2-\lambda)(3-\lambda)-0=0$
$\lambda =2,\lambda =3 $
The eigen values of A are 2, 3
Now the eigen vaues of $A^{-1}$ are, $A^{-1}=\frac{1}{2} \ and \ \frac{1}{3} $
For $6A^{-1} = 6(\frac{1}{2}) \ and \ 6 (\frac {1}{3})$
$6A^{-1}=3 \ and \ 2$-------(1)
similarly eigen values of $A^{3} $ are
$A^{3}=(2)^3$ and $(3)^{3}$
$A^{3}$ =9 and 27 --------(2)
and for $2I = 2(1) =2$-----(3)
Hence eigen values for
i) $6A^{-1} + A^3 +2I $
=$3+9+2$
=$14$
ii) $6A^{-1} +A^3+2I$
=$2+27+2$
=$31$
Therefore eigen values for $6A^{-1}+A^{3}+2I$ is $14 \ and \ 31.$
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