Question:
If $A=\operatorname{diag}(1,2,3)$, then $|A|=$_______
Solution:
Given: $A=\operatorname{diag}(1,2,3)$
If $A=\operatorname{diag}(a, b, c)$, then $|A|=a \times b \times c$.
Thus, if $A=\operatorname{diag}(1,2,3)$, then $|A|=1 \times 2 \times 3=6$.
Hence, $|A|=\underline{6}$.