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JEE Main & Advanced Sample Paper JEE Main - Mock Test - 8

  • question_answer
    In the expansion of\[{{\left( x-\frac{1}{x} \right)}^{6}}\], the constant term is

    A) -20       

    B) 20   

    C) 30                    

    D) -30

    Correct Answer: A

    Solution :

    [a] : In the expansion of\[{{\left( x-\frac{1}{x} \right)}^{6}}\], the general term is \[^{6}{{C}_{r}}{{x}^{6-r}}{{\left( -\frac{1}{x} \right)}^{r}}={}^{6}{{C}_{r}}{{(-1)}^{r}}{{x}^{6-2r}}\]. For term independent of \[x,6-2r=0\Rightarrow r=3\] So, the required constant term \[={{(-1)}^{3}}{{.}^{6}}{{C}_{3}}=-20\]


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