Question: The trace of the matrix $A=\left[\begin{array}{rrr}1 & -5 & 7 \\ 0 & 7 & 9 \\ 11 & 8 & 9\end{array}\right]$ is
(a) 17
(b) 25
(c) 3
(d) 12
Solution:
(a) 17
The trace of a matrix is the sum of the diagonal elements.
$\therefore \operatorname{Tr}(A)=1+7+9=17$
