JEE Main & Advanced JEE Main Paper (Held On 9 April 2017)

  • question_answer
    The coefficient of \[{{x}^{-5}}\] in the binomial expansion of \[{{\left( \frac{x+1}{{{x}^{\frac{2}{3}}}-{{x}^{\frac{1}{3}}}+1}\,-\frac{x-1}{x-{{x}^{\frac{1}{2}}}} \right)}^{10}}\] where \[x\ne 0,1\] is:     [JEE Online 09-04-2017]

    A)  -1                                          

    B)  4

    C)  3                                            

    D)  - 4

    Correct Answer: C

    Solution :

    \[{{\left[ \frac{({{x}^{1/3}}+1)\,({{x}^{2/3}}-{{x}^{1/3}}+1)}{({{x}^{2/3}}-{{x}^{1/3}}+1)}-\frac{(\sqrt{x}-1)(\sqrt{x}+1)}{\sqrt{x}(\sqrt{x}-1)} \right]}^{10}}\] \[={{({{x}^{1/3}}\,+1-1-1/{{x}^{1/2}})}^{10}}\] \[=({{x}^{1/3}}\,-1/{{x}^{1/2}})\]                              \[r=1/3,\,b=1/2\] \[r=\frac{\frac{10}{3}-(-5)}{1/3+\frac{1}{2}}\] \[r=\frac{25/3}{\left( 5\frac{1}{2} \right)}\,=10\] \[\cos .\,=10{{c}_{10}}\,(1)\,{{(-1)}^{10}}\,=1\]


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