$$ \begin{matrix} 1 & 1 & 0 \\ 3 & 0 & 1 \\ 1 & -1 & 2 \\ \end{matrix} $$$$ \begin{bmatrix} 1 & 1 & 0 \\ 3 & 0 & 1 \\ 1 & -1 & 2 \\ \end{bmatrix} $$
Is the 3$3$ by 3$3$ matrix above diagonalizable given the eigenvalues -1$-1$ and 2$2$? There are only 2 eigenvalue$2$ eigenvalues so the one with the multiplicity of two needs a full rank eigenspace for this to be diagonalizable. I think there should be a way to tell from the matrix alone whether that's possible without doing all the row operations, but I'm not sure what I should be looking for.