J & K CET Engineering J and K - CET Engineering Solved Paper-2009

  • question_answer
    If  \[\hat{i}-\hat{k},\,\lambda \hat{i}+\hat{j}+(1-\lambda )\hat{k}\]  and \[\mu \hat{i}+\lambda \hat{j}+(1+\lambda -\mu )\hat{k}\]are three coterminal edges of a parallelopiped, then its volume depends on

    A)  only \[\lambda \]          

    B)  only \[\mu \]

    C)  both \[\lambda \] and \[\mu \]

    D)  neither \[\lambda \] nor\[\mu \] 

    Correct Answer: D

    Solution :

    Given edges are \[\vec{a}=\hat{i}-\hat{k},\,\,\vec{b}=\lambda \hat{i}+\hat{j}+(1-\lambda )\hat{k}\] and \[\vec{c}=\mu \hat{i}+\lambda \hat{j}+(1+\lambda -\mu )\hat{k}\] \[\therefore \]   Volume of parallelepiped \[=[\vec{a}\,\vec{b}\,\vec{c}]\] \[=\left| \begin{matrix}    1 & 0 & -1  \\    \lambda  & 1 & 1-\lambda   \\    \mu  & \lambda  & 1+\lambda -\mu   \\ \end{matrix} \right|\] \[=1(1+\lambda -\mu -\lambda +{{\lambda }^{2}})-0-1({{\lambda }^{2}}-\mu )\] \[=1+{{\lambda }^{2}}-\mu -{{\lambda }^{2}}+\mu \] \[=1\] Hence, volume depends on neither \[\lambda \] nor \[\mu \].


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