JEE Main & Advanced JEE Main Paper (Held On 11-Jan-2019 Morning)

  • question_answer
    The sum of the real values of x for which the middle term in the binomial expansion of\[{{\left( \frac{{{x}^{3}}}{3}+\frac{3}{x} \right)}^{8}}\]equal 5670 is [JEE Main Online Paper (Held On 11-Jan-2019 Morning]

    A) 8                                 

    B)               6     

    C)               0                                             

    D)               4

    Correct Answer: C

    Solution :

    Given binomial expansion is\[{{\left( \frac{{{x}^{3}}}{3}+\frac{3}{x} \right)}^{8}}\] So, middle term \[{{T}_{5}}{{=}^{8}}{{C}_{4}}{{\left( \frac{{{x}^{3}}}{3} \right)}^{4}}.{{\left( \frac{3}{x} \right)}^{4}}=5670\] \[\Rightarrow \]\[^{8}{{C}_{4}}\frac{{{x}^{12}}}{{{3}^{4}}}.\frac{{{3}^{4}}}{{{x}^{4}}}=5670\] \[\Rightarrow \]\[70{{x}^{8}}=5670\] \[\Rightarrow \]\[{{x}^{8}}=81\]\[\Rightarrow \]\[x=\pm \sqrt{3}\] \[\therefore \]Sum of real values of x is 0.


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