JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2006

  • question_answer
        Given that\[|\overrightarrow{a}|=3,|\overrightarrow{b}|=4,|\overrightarrow{a}\times \overrightarrow{b}|=10,\]then\[|\overrightarrow{a}.\overrightarrow{b}{{|}^{2}}\]equals

    A)  88                                         

    B)  44

    C)  22                                         

    D)  none of these

    Correct Answer: B

    Solution :

                    Key Idea: \[|\overrightarrow{a}\times \overrightarrow{b}{{|}^{2}}+|\overrightarrow{a}.\overrightarrow{b}{{|}^{2}}=|\overrightarrow{a}{{|}^{2}}|\overrightarrow{b}{{|}^{2}}\] Given \[|\overrightarrow{a}\times \overrightarrow{b}{{|}^{2}}=10,|\overrightarrow{a}|=3,|\overrightarrow{b}|=4\] \[\Rightarrow \]               \[{{(10)}^{2}}+|\overrightarrow{a}.\overrightarrow{b}{{|}^{2}}={{(3)}^{2}}.{{(4)}^{2}}\] \[\Rightarrow \] \[|\overrightarrow{a}.\overrightarrow{b}{{|}^{2}}=9\times 16-100=144-100\] \[\Rightarrow \]               \[|\overrightarrow{a}.\overrightarrow{b}{{|}^{2}}=44\]


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