Question
Find eigenvalues of matrix:
$$ A = \left[ \begin{matrix}3&-1&1\\-1&4&2\\1&2&4\end{matrix} \right] $$Answer
The eigenvalues of matrix A are:
$$ \lambda_1 = 1 ~ \text{ , } ~ \lambda_2 = 4 ~ \text{ and } ~ \lambda_3 = 6 $$Explanation
Step 1 : The characteristic polynomial for matrix A is:
$$ p(\lambda) = -\lambda^3+11\lambda^2-34\lambda+24 $$
Step 2 : Eigenvalues are roots of the characteristic polynomial, so the equation
$$ -\lambda^3+11\lambda^2-34\lambda+24 = 0 $$yields the above eigenvalues.
( click here to view an explanation on how to solve this equation.)
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