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I have a matrix (2 5, -1 4) and need to solve for the complex eigenvalues. My problem is.. I'm not getting complex numbers.

(I will be using x in place of lambda since I don't know how to use that symbol)

I take the determinate of (2-x 5, -1 4-x) and I arrive at a quadratic equation of x^2 - 6x +8. If I set that to 0, well, my eigenvalues are real. I know they're not real, and if I use online calculators such as wolframalpha's (http://www.wolframalpha.com/widgets/view.jsp?id=3f00f874e9837b0ec850a34c85432d66) It computes complex eigenvalues. What am I missing?

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determinant of of $(2-x , 5 ; -1 , 4-x)$ is $x^2 - 6x +13$, not $x^2 - 6x +8$ .

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