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J & K CET Engineering J and K - CET Engineering Solved Paper-2013

  • question_answer
    If the position vector a of a point \[(12,\,\,n)\] is such that \[|a|=13,\] then the value of \[\pi \] is

    A)  \[\pm \,\,3\]                   

    B)  \[\pm \,\,4\]

    C)  \[\pm \,\,5\]                   

    D)  \[\pm \,\,6\]

    Correct Answer: C

    Solution :

    Given, Position vector of \[a=12\,\hat{i}+n\hat{j}\] Also; \[|a|=13\] \[\Rightarrow \] \[|12\hat{i}+n\hat{j}|=13\] \[\Rightarrow \] \[\sqrt{144+{{n}^{2}}}=13\] \[\Rightarrow \] \[144+{{n}^{2}}=169\] \[\Rightarrow \] \[{{n}^{2}}=25\] \[\therefore \] \[n=\pm 5\]


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