Solution
= Solution
The <trace> is the sum of the <eigenvalues>, counting multiplicity, while the <determinant> is their product:
$$
\boxed{\operatorname{tr}A=1-2+1=0=4-2-2,\qquad
\det A=16=4(-2)(-2)}.
$$
A direct expansion along the middle row checks the latter: $(-2)(1-9)=16$.