11th Class Mathematics Sample Paper Mathematics Olympiad - Sample Paper-6

  • question_answer
    Constant term of the expansion of \[{{\left( \mathbf{x}-\frac{1}{x} \right)}^{10}}\]is

    A)  152                 

    B)  \[-152\]         

    C)  252                             

    D)  \[-252\]

    Correct Answer: D

    Solution :

    [d] \[n=10=\]even So, number of terms in the given expression \[{{\left( x-\frac{1}{x} \right)}^{10}}\]is 11 i.e. \[{{t}_{6}}\] be constant term of the expression. So, constant term \[{{=}^{10}}{{C}_{5}}.{{(x)}^{5}}.{{\left( -\frac{1}{x} \right)}^{5}}\] \[={{-}^{10}}{{C}_{5}}=\frac{-10\times 9\times 8\times 7\times 6}{5\times 4\times 3\times 2}\] \[=-3\times 2\times 7\times 6=-252\] .Hence, option [d] is correct.


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