RAJASTHAN ­ PET Rajasthan PET Solved Paper-2010

  • question_answer
    If the planes\[\overrightarrow{r}.(2\hat{i}+\lambda \hat{j}-3\hat{k})=0\]and\[\overrightarrow{r}.(\lambda \hat{i}-3\hat{j}+\hat{k})=5\]are perpendicular, then value of\[\lambda \]is

    A)  2                  

    B)  \[-2\]

    C)  3                

    D)  \[-3\]

    Correct Answer: D

    Solution :

     Given planes are \[\overrightarrow{r}.(2\hat{i}+\lambda \hat{j}-3\hat{k})=0\] and \[\overrightarrow{r}.(\lambda \hat{i}-3\hat{j}+\hat{k})=5\] Here,          \[{{\overrightarrow{n}}_{1}}=2\hat{i}+\lambda \hat{j}-3\hat{k}\] and         \[{{\overrightarrow{n}}_{2}}=\lambda \hat{i}-3\hat{j}+\hat{k}\] Since both of the planes are perpendicular. \[\therefore \] \[{{\overrightarrow{n}}_{1}}.{{\overrightarrow{n}}_{2}}=0\] \[\Rightarrow \] \[2\lambda -3\lambda -3=0\] \[\Rightarrow \] \[\lambda =-3\]


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