JEE Main & Advanced Sample Paper JEE Main - Mock Test - 33

  • question_answer
    The integer just greater than \[{{(3+\sqrt{5})}^{2n}}\] is divisible by \[(n\in N)\]

    A) \[{{2}^{n-1}}\]           

    B)        \[{{2}^{n+1}}\]

    C) \[{{2}^{n+2}}\]                     

    D)        not divisible by 2

    Correct Answer: B

    Solution :

    \[R={{(3+\sqrt{5})}^{2n}},\,\,G\,\,=\,\,{{(3-\sqrt{5})}^{2n}}\] Let \[\left[ R \right] + 1 = I\] (\[\because \] [.] greatest integer function) \[\Rightarrow \,\,\,R+G=I\,\,\,\,\,\,\,\,\,(\because \,\,\,0<G<1)\] \[{{(3+\sqrt{5})}^{2n}}+{{(3-\sqrt{5})}^{2n}}=\,\,I\] seeing the option put \[\operatorname{n}= 1\] \[\operatorname{I} = 28 is divisible by 4 i.e. {{2}^{n+1}}\]


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