J & K CET Engineering J and K - CET Engineering Solved Paper-2008

  • question_answer
    If \[{{C}_{0}},{{C}_{1}},{{C}_{2}},.....{{C}_{n}}\] denotes the binomial coefficients in the expansion of \[{{(1+x)}^{n}},\]then \[{{C}_{0}}+\frac{{{C}_{1}}}{2}+\frac{{{C}_{2}}}{3}+....+\frac{{{C}_{n}}}{n+1}\] is equal to

    A)  \[\frac{{{2}^{n+1}}-1}{n+1}\]

    B)  \[\frac{{{2}^{n}}-1}{n}\]

    C)  \[\frac{{{2}^{n-1}}-1}{n-1}\]

    D)  \[\frac{{{2}^{n+1}}-1}{n+2}\]

    Correct Answer: A

    Solution :

    We know, \[{{(1+x)}^{n}}={{C}_{0}}+{{C}_{1}}x+{{C}_{2}}{{x}^{2}}+....+{{C}_{n}}{{x}^{n}}\] On integrating both sides 0 to 1, we get \[\left[ \frac{{{(1+x)}^{n+1}}}{n+1} \right]_{0}^{1}\] \[=\left[ {{C}_{0}}x+\frac{{{C}_{1}}{{x}^{2}}}{2}+\frac{{{C}_{2}}{{x}^{3}}}{3}+....+\frac{{{C}_{n}}{{x}^{n+1}}}{n+1} \right]_{0}^{1}\] \[\Rightarrow \] \[\frac{{{2}^{n+1}}-1}{n+1}={{C}_{0}}+\frac{{{C}_{1}}}{2}+\frac{{{C}_{2}}}{3}+.....+\frac{{{C}_{n}}}{n+1}\]


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