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

  • question_answer
    \[(\mathbf{a}-\mathbf{b})\times (\mathbf{a}+\mathbf{b})=\]                                      [MP PET 1987]

    A)                 \[2(\,\mathbf{a}\times \mathbf{b})\]  

    B)                 \[\mathbf{a}\times \mathbf{b}\]

    C)                 \[{{a}^{2}}-{{b}^{2}}\]

    D)                 None of these

    Correct Answer: A

    Solution :

               \[(\mathbf{a}-\mathbf{b})\times (\mathbf{a}+\mathbf{b})=\mathbf{a}\times \mathbf{a}-\mathbf{b}\times \mathbf{a}+\mathbf{a}\times \mathbf{b}-\mathbf{b}\times \mathbf{b}\]                                            \[=\mathbf{a}\times \mathbf{b}-\mathbf{b}\times \mathbf{a}=\mathbf{a}\times \mathbf{b}+\mathbf{a}\times \mathbf{b}=2(\mathbf{a}\times \mathbf{b}).\]


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