\left| \begin{array}{ccc}
 7 & -2 & 1 \\
 2 & 1 & 1 \\
 3 & 2 & 2
\end{array}\right|
=
\left|\begin{array}{ccc}
 7 & -2 & 1 \\
 2 & 1 & 1 \\
 3 & 2 & 2
\end{array}\right|
\text{ }
\begin{array}{cc}
 7 & -2 \\
 2 & 1 \\
 3 & 2
\end{array}
=7*1*2-2*1*3+1*2*2-3*1*1-2*1*7-2*2*(-2)=14-6+4-3-14+8=3