JEE Main & Advanced Mathematics Vector Algebra Question Bank Vector or Cross product of two vectors and its application

  • question_answer
    A unit vector perpendicular to each of the vector \[2\mathbf{i}-\mathbf{j}+\mathbf{k}\] and \[3\mathbf{i}+4\mathbf{j}-\mathbf{k}\] is equal to                                  [MP PET 2003]

    A)                 \[\frac{(-3\mathbf{i}+5\mathbf{j}+11\mathbf{k})}{\sqrt{155}}\]              

    B)                 \[\frac{(3\mathbf{i}-5\mathbf{j}+11\mathbf{k})}{\sqrt{155}}\]

    C)                 \[\frac{(6\mathbf{i}-4\mathbf{j}-\mathbf{k})}{\sqrt{53}}\]          

    D)                 \[\frac{(5\mathbf{i}+3\mathbf{j})}{\sqrt{34}}\]

    Correct Answer: A

    Solution :

               Let \[\mathbf{a}=2\mathbf{i}-\mathbf{j}+\mathbf{k}\] and \[\mathbf{b}=3\mathbf{i}+4\mathbf{j}-\mathbf{k},\] then a unit vector perpendicular to \[\mathbf{a}\] and \[\mathbf{b}\] is \[\frac{\mathbf{a}\times \mathbf{b}}{|\mathbf{a}\times \mathbf{b}|}\]            Here \[\mathbf{a}\times \mathbf{b}=-3\mathbf{i}+5\mathbf{j}+11\mathbf{k}\]                 Unit vector is \[\frac{-3\mathbf{i}+5\mathbf{j}+11\mathbf{k}}{\sqrt{155}}\].


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