JEE Main & Advanced AIEEE Solved Paper-2004

  • question_answer
    If\[A\times B=B\times A,\]then the angle between A and B is     AIEEE  Solved  Paper-2004

    A) \[\pi \]           

    B)                        \[\pi /3\]             

    C)        \[\pi /2\]                   

    D)        \[\pi /4\]

    Correct Answer: A

    Solution :

    Given, \[(A\times B)=(B\times A)\] \[\Rightarrow \]\[(A\times B)-(B\times A)=0\] or \[(A\times B)+(A\times B)=0\]                                                 \[[\because (B\times A)=-(A\times B)]\] \[\Rightarrow \]\[2(A\times B)=0\] \[\Rightarrow \]\[2AB\sin \theta =0\] \[\Rightarrow \]\[\sin \theta =0\]                                 \[(\because |A|=A\ne 0,|B|=B\ne 0)\] \[\therefore \]  \[\theta =0\]or \[\pi \] 


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