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