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NEET Sample Paper NEET Sample Test Paper-11

  • question_answer
    The angle between the two vectors\[\vec{A}=3\hat{i}+4\hat{j}+5\hat{k}\]and\[\vec{B}=3\hat{i}+4\hat{j}-5\hat{k}\]  will be

    A)  zero                             

    B)  \[{{45}^{o}}\]

    C) \[{{90}^{o}}\]                        

    D) \[{{180}^{o}}\]

    Correct Answer: C

    Solution :

    \[\vec{A}=3\hat{i}+4\hat{j}+5\hat{k},\vec{B}=3\hat{i}+4\hat{j}-5\hat{k}\] \[\vec{A}.\vec{B}=(3\hat{i}+4\hat{j}+5\hat{k}).(3\hat{i}+4\hat{j}-5\hat{k})\] \[|\vec{A}||\vec{B}|cos\theta =9+16-25=0\] \[|\vec{A}|\ne 0,|\vec{B}|\ne 0,\]hence, \[\cos \theta =0,\theta ={{90}^{o}}\]


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