Shortcut for calculating eigenvalues

For 2x2 matrix see A quick trick for computing eigenvalues | Chapter 15, Essence of linear algebra

So for the eigenvalues in 3, m = average of the diagonals (the trace). p is the determinant. You can verify those values for the matrix shown in bottom right. Eigenvalues are 10 and 4 after plugging into the formula.

Thanks for the information.

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