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

  • question_answer
    If three conterminous edges of a parallelopiped are represented by \[\mathbf{a}-\mathbf{b},\,\,\mathbf{b}-\mathbf{c}\] and \[\mathbf{c}-\mathbf{a}\], then its volume is                                       [MP PET 1999; Pb. CET 2003]

    A)             [a b c]

    B)             2 [a b c]

    C)             \[\,{{[\mathbf{a}\,\,\mathbf{b}\,\,\mathbf{c}]}^{2}}\]

    D)             0

    Correct Answer: D

    Solution :

                    \[(\mathbf{a}-\mathbf{b})\,.\,(\mathbf{b}-\mathbf{c})\times (\mathbf{c}-\mathbf{a})=(\mathbf{a}-\mathbf{b})\,.\,(\mathbf{b}\times \mathbf{c}-\mathbf{b}\times \mathbf{a}+\mathbf{c}\times \mathbf{a})\]                 \[=\mathbf{a}\,.\,(\mathbf{b}\times \mathbf{c})-\mathbf{a}\,.\,(\mathbf{b}\times \mathbf{a})+\mathbf{a}\,.\,(\mathbf{c}\times \mathbf{a})\] \[-\mathbf{b}\,.\,(\mathbf{b}\times \mathbf{c})+\mathbf{b}\,.\,(\mathbf{b}\times \mathbf{a})-\mathbf{b}\,.\,(\mathbf{c}\times \mathbf{a})\] =0.


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