JCECE Engineering JCECE Engineering Solved Paper-2009

  • question_answer
    \[\overset{\to }{\mathop{\mathbf{A}}}\,\cdot \{(\overset{\to }{\mathop{\mathbf{B}}}\,+\overset{\to }{\mathop{\mathbf{C}}}\,)\times (\overset{\to }{\mathop{\mathbf{A}}}\,+\overset{\to }{\mathop{\mathbf{B}}}\,+\overset{\to }{\mathop{\mathbf{C}}}\,)\}\]equals

    A) \[[\overset{\to }{\mathop{\mathbf{A}}}\,\overset{\to }{\mathop{\mathbf{B}}}\,\overset{\to }{\mathop{\mathbf{C}}}\,]\]                     

    B) \[[\overset{\to }{\mathop{\mathbf{B}}}\,\overset{\to }{\mathop{\mathbf{A}}}\,\overset{\to }{\mathop{\mathbf{C}}}\,]\]

    C) \[0\]                                     

    D) \[1\]

    Correct Answer: C

    Solution :

    \[\overset{\to }{\mathop{\mathbf{A}}}\,\cdot \{(\overset{\to }{\mathop{\mathbf{B}}}\,+\overset{\to }{\mathop{\mathbf{C}}}\,)\times (\overset{\to }{\mathop{\mathbf{A}}}\,+\overset{\to }{\mathop{\mathbf{B}}}\,+\overset{\to }{\mathop{\mathbf{C}}}\,)\}\] \[=\overset{\to }{\mathop{\mathbf{A}}}\,\cdot \{\overset{\to }{\mathop{\mathbf{B}}}\,\times \overset{\to }{\mathop{\mathbf{A}}}\,+\overset{\to }{\mathop{\mathbf{0}}}\,+\overset{\to }{\mathop{\mathbf{B}}}\,\times \overset{\to }{\mathop{\mathbf{C}}}\,+\overset{\to }{\mathop{\mathbf{C}}}\,\times \overset{\to }{\mathop{\mathbf{A}}}\,+\overset{\to }{\mathop{\mathbf{C}}}\,\times \overset{\to }{\mathop{\mathbf{B}}}\,+\overset{\to }{\mathop{\mathbf{0}}}\,\}\] \[=[\overset{\to }{\mathop{\mathbf{A}}}\,\overset{\to }{\mathop{\mathbf{B}}}\,\overset{\to }{\mathop{\mathbf{A}}}\,]+[\overset{\to }{\mathop{\mathbf{A}}}\,\overset{\to }{\mathop{\mathbf{B}}}\,\overset{\to }{\mathop{\mathbf{C}}}\,]+[\overset{\to }{\mathop{\mathbf{A}}}\,\overset{\to }{\mathop{\mathbf{C}}}\,\overset{\to }{\mathop{\mathbf{A}}}\,]-[\overset{\to }{\mathop{\mathbf{A}}}\,\overset{\to }{\mathop{\mathbf{B}}}\,\overset{\to }{\mathop{\mathbf{C}}}\,]\] \[=0\]


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