Finding eigenvectors with complex eigenvalue

complex numberseigenvalues-eigenvectorslinear algebramatrices

I have trouble with how to find eigenvectors when you have a complex eigenvalue

For example the matrix
$$ \begin{pmatrix}
0 & 1\\
-2 & -2
\end{pmatrix}$$

Here you get the eigenvalues $-1$ and $ \pm i$

Where do i go from here to find a eigenvector. The solution says it should be the 2×1 matrix:
$$\begin{pmatrix}
1\pm i \\
-2
\end{pmatrix}$$

Best Answer

You do it just as you would for real eigenvalues.

For instance, if you want an eigenvector corresponding to the eigen value $-1+i$, you solve the system$$\left\{\begin{array}{ll}y=(-1+i)x\\-2x-2y=(-1+i)y,\end{array}\right.$$you will get that the solutions are the vectors of the form $\bigl((1+i)x,-2x\bigr)$. In particular, $(1+i,-2)$ is an eigenvector corresponding to the eigenvalue $-1+i$.

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