J & K CET Engineering J and K - CET Engineering Solved Paper-2007

  • question_answer
    The area of a parallelogram having diagonals \[\vec{a}=3\hat{i}+\hat{j}-2\hat{k}\] and \[\vec{b}=\hat{i}-3\hat{j}+4\hat{k}\] is

    A)  \[10\sqrt{3}\]         

    B)  \[5\sqrt{3}\]

    C)  \[8\]            

    D)  \[4\]

    Correct Answer: B

    Solution :

    Area of parallelogram \[=\frac{1}{2}|\vec{a}\times \vec{b}|\] \[=\frac{1}{2}\left\| \begin{matrix}    {\hat{i}} & {\hat{j}} & {\hat{k}}  \\    3 & 1 & -2  \\    1 & -3 & 4  \\ \end{matrix} \right\|=\frac{1}{2}\left| \{\hat{i}(-2)-\hat{j}(14)+\hat{k}(-10)\} \right|\] \[=|-\hat{i}-7\hat{j}-5\hat{k}|=\sqrt{1+49+25}\] \[=\sqrt{75}=5\sqrt{3}\]


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