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JEE Main & Advanced Mathematics Vector Algebra Question Bank Modulus of vector Algebra of vectors

  • question_answer
    The position vectors of P and Q are \[5\mathbf{i}+4\mathbf{j}+a\mathbf{k}\] and \[-\mathbf{i}+2\mathbf{j}-2\mathbf{k}\] respectively. If the distance between them is 7, then the value of a will be

    A) 5, 1

    B) 5, 1

    C) 0, 5        

    D) 1, 0

    Correct Answer: A

    Solution :

    \[7=\sqrt{{{(5+1)}^{2}}+{{(4-2)}^{2}}+{{(a+2)}^{2}}}\Rightarrow a+2=\pm 3\] or \[a\,=-5,\,\,1.\]          


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