JEE Main & Advanced JEE Main Paper (Held On 9 April 2016)

  • question_answer
    For\[x\in R,x=-1,\]if \[{{(1+x)}^{2016}}+x{{(1+x)}^{2015}}+{{x}^{2}}\]\[{{(1+x)}^{2014}}+...........+{{x}^{2016}}=\]\[\sum\limits_{i=0}^{2016}{{{a}_{i}}{{x}^{i}},}\]then\[{{a}_{17}}\]is equal to:   JEE Main Online Paper (Held On 09 April 2016)

    A) \[\frac{2016!}{16!}\]                      

    B) \[\frac{2017!}{2000!}\]

    C) \[\frac{2017!}{17!2000!}\]

    D) \[\frac{2016!}{17!1999!}\]

    Correct Answer: C

    Solution :

    \[\sum\limits_{i=0}^{2016}{{{c}_{i}}.{{x}^{i}}={{(1+x)}^{2016}}+x{{(1+x)}^{2016}}+{{x}^{2}}{{(1+x)}^{2014}}}\]\[+..........+{{x}^{2016}}\] \[=\frac{{{(1+x)}^{2016}}\left( 1-{{\left( \frac{x}{1+x} \right)}^{2017}} \right)}{1-\frac{x}{1+x}}\] \[\frac{=\frac{{{(1+x)}^{2016}}}{1}-\frac{{{x}^{2017}}}{(1+x)}}{\frac{x+1-x}{1+x}}=\frac{{{(1+x)}^{2017}}-{{x}^{2017}}}{1}\] \[\therefore \]\[{{a}_{17}}{{=}^{2017}}{{C}_{17}}=\frac{2007!}{17!2000!}\]                                


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