JEE Main & Advanced Mathematics Vector Algebra Question Bank Vector or Cross product of two vectors and its application

  • question_answer
    The area of a parallelogram whose two adjacent sides are represented by the vector \[3\mathbf{i}-\mathbf{k}\] and \[\mathbf{i}+2\mathbf{j}\] is   [MNR 1981]

    A)                 \[\frac{1}{2}\sqrt{17}\]

    B)                 \[\frac{1}{2}\sqrt{14}\]

    C)                 \[\sqrt{41}\]

    D)                 \[\frac{1}{2}\sqrt{7}\]

    Correct Answer: C

    Solution :

               The area of parallelogram is given by \[=|\overrightarrow{AB}\times \overrightarrow{AD}|\] \[=\frac{1}{2}|\overrightarrow{AC}\times \overrightarrow{BD}|\]            Here we are given adjacent sides and so            \[\overrightarrow{AB}\times \overrightarrow{AD}=\left| \begin{matrix}    \mathbf{i} & \mathbf{j} & \mathbf{k}  \\    3 & 0 & -1  \\    1 & 2 & 0  \\ \end{matrix} \right|=2\mathbf{i}-\mathbf{j}+6\mathbf{k}\]                                 Hence required area is \[=|2\mathbf{i}-\mathbf{j}+6\mathbf{k}|=\sqrt{41}.\]


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