JEE Main & Advanced Mathematics Functions Question Bank Limits

  • question_answer
    If \[{{a}_{1}}=1\] and \[{{a}_{n+1}}=\frac{4+3{{a}_{n}}}{3+2{{a}_{n}}},\ n\ge 1\] and if \[-\frac{1}{3}\], then the value of a is

    A)                 \[\sqrt{2}\]

    B)                 \[-\sqrt{2}\]

    C)                 2

    D)                 None of these

    Correct Answer: A

    Solution :

                       We have \[{{a}_{n+1}}=\frac{4+3{{a}_{n}}}{3+2{{a}_{n}}}\]            \[\Rightarrow \,\,\underset{n\to \infty }{\mathop{\lim }}\,\,{{a}_{n+1}}=\underset{n\to \infty }{\mathop{\lim }}\,\,\frac{4+3{{a}_{n}}}{3+2{{a}_{n}}}\]            \[\Rightarrow \,\,a=\frac{4+3a}{3+2a}\,\Rightarrow 2{{a}^{2}}=4\,\,\Rightarrow \,\,a=\sqrt{2}\]                                 \[a\ne -\sqrt{2}\] because each \[{{a}_{n}}>0,\] therefore \[\lim \,{{a}_{n}}=a>0.\]


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