1.1.12 Vector Algebra
Problem:
Calculate the area of the parallelogram formed by the vectors \( \vec{a} \) and \( \vec{b} \).
\[
\begin{array}{l}
\vec{a}=7 \vec{p}+\vec{q}, \quad \vec{b}=\vec{p}-3 \vec{g}, \quad|\vec{p}|=3, \\
|\vec{q}|=1, \quad\left(\widehat{\vec{p}, \vec{q})}=\frac{3 \pi}{4} .\right.
\end{array}
\]