JEE Main & Advanced Mathematics Vector Algebra Question Bank Scalar triple product and their applications

  • question_answer
    If \[\mathbf{x}\,.\,\mathbf{a}=0,\,\,\mathbf{x}\,.\,\mathbf{b}=0\] and \[\mathbf{x}\,.\,\mathbf{c}=0\] for some non-zero vector x, then the ture statement is [IIT 1983; Karnataka CET 2002]

    A)             \[[\mathbf{a}\,\,\mathbf{b}\,\,\mathbf{c}]=0\]

    B)             \[[\mathbf{a}\,\,\mathbf{b}\,\,\mathbf{c}]\ne 0\]

    C)             \[[\mathbf{a}\,\,\mathbf{b}\,\,\mathbf{c}]=1\]

    D)             None of these

    Correct Answer: A

    Solution :

                    Since \[\mathbf{x}\]is a non-zero vector, the given conditions will be satisfied, if either (i) at least one of the vectors \[\mathbf{a},\,\,\mathbf{b},\,\,\mathbf{c}\] is zero or (ii) \[\mathbf{x}\] is perpendicular to all the vectors \[\mathbf{a},\,\,\mathbf{b},\,\,\mathbf{c}.\] In case (ii), \[\mathbf{a},\,\,\mathbf{b},\,\,\mathbf{c}\] are coplanar and so \[[\mathbf{a}\,\,\mathbf{b}\,\,\mathbf{c}]=0.\]


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