Question $1$

$2\mathrm{.}5$ pts

Let $=([20,9,2\mathrm{.}5],[9,19,3],[2\mathrm{.}5,3,23])$

Q$1.$ Let ${}_1=30\mathrm{.}5$ and ${}_2=21$ be the top two eigenvalues of $.$ What is ${}_3?$