c
સમાંતરબાજુ ચતુષ્કોણનું ક્ષેત્રફળ \( = {\mkern 1mu} {\mkern 1mu} \left| {\left. {\vec A \times {\mkern 1mu} \vec B} \right|} \right.{\mkern 1mu} {\mkern 1mu}  = {\mkern 1mu} \left| {\left. {\begin{array}{*{20}{c}}
  {\hat i}&{\hat j}&{\hat k} \\ 
  3&1&0 \\ 
  0&1&2 
\end{array}} \right|} \right.\)

\( = |2\hat i{\mkern 1mu} {\mkern 1mu}  - 6\hat j + \;{\mkern 1mu} 3\hat k|\)

\({\mkern 1mu}  = \sqrt {{2^2} + \;{{\left( { - 6} \right)}^2}{\mkern 1mu} {\mkern 1mu}  + \;{\mkern 1mu} {3^2}}  = 7\)