JEE Main & Advanced Mathematics Binomial Theorem and Mathematical Induction Question Bank Properties of binomial coefficients

  • question_answer
    \[^{n}{{C}_{0}}-\frac{1}{2}{{\,}^{n}}{{C}_{1}}+\frac{1}{3}{{\,}^{n}}{{C}_{2}}-......+{{(-1)} ^{n}}\frac{^{n}{{C}_{n}}}{n+1}=\]

    A) n

    B) 1/n

    C) \[\frac{1}{n+1}\]

    D) \[\frac{1}{n-1}\]

    Correct Answer: C

    Solution :

    Trick: Put \[n=\] 1, 2 At  \[n=1,{{\,}^{1}}{{C}_{0}}-\frac{1}{2}{{\,}^{1}}{{C}_{1}}=1-\frac{1}{2}=\frac{1}{2}\] At  \[n=2,\,{{\,}^{2}}{{C}_{0}}-\frac{1}{2}\,{{\,}^{2}}{{C}_{1}}+\frac{1}{3}{{\,}^{2}}{{C}_{2}}=1-1+\frac{1}{3}=\frac{1}{3}\] which is given by option C.


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