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$\begin{bmatrix} a\\\\b\end{bmatrix}\longmapsto \begin{bmatrix}-3&1\\\\0&2\end{bmatrix} \begin{bmatrix} a\\\\b\end{bmatrix}$

Use the characteristic polynomail to find all eigenvalues for the transformation for each eigenvalues $\lambda$ find all eigenvectors with eigenvalues $\lambda$ and find a basis for $E_\lambda$

Here is what I have so far

$\chi_f(x)=\begin{bmatrix}-3-x&1\\\\0&2-x\end{bmatrix}$ $=(-3-x)(2-x)$ so there are two eigenvalues $\lambda=-3$ and $\lambda=2$

I'm not sure how to find a basis for these eigenvalues though

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    Well, that means $b=0$, clearly =) See my answer2012-12-03

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To find the subspaces you're looking after you ought to solve the homogeneous system that you obtain by plugging in the eigenvalues. First, note your eigenvalues are wrong. The two roots of $\chi_f(x)$ are $-3$ and $2$, which are precisely those values for which $(-3-x)(2-x)-1\cdot 0=0$. Thus you get that the equations of the spaces are

For $E_{2}$ you get

$-5x+y=0$

Thus $5x=y$ and the space is generated by $(5,1)$. In the other case, that is $E_{-3}$, you get

$0x+y=0$ $0x+5y=0$

Thus, you have $x$ free (it doesn't appear in the equations) and need $y=0$. Whence, the space is generated by $(1,0)$.