JEE Main & Advanced Mathematics Binomial Theorem and Mathematical Induction Question Bank Mock Test - Binomial Theorem

  • question_answer
    \[1+\frac{1}{3}x+\frac{1\times 4}{3\times 6}{{x}^{2}}+\frac{1\times 4\times 7}{3\times 6\times 9}{{x}^{3}}+...\]is equal to

    A) x                     

    B) \[{{(1+x)}^{1/3}}\]

    C) \[{{(1-x)}^{1/3}}\]     

    D) \[{{(1-x)}^{-1/3}}\]

    Correct Answer: D

    Solution :

    [d] Let \[{{(1+y)}^{n}}=1+\frac{1}{3}x+\frac{1\times 4}{3\times 6}{{x}^{2}}+\frac{1\times 4\times 7}{3\times 6\times 9}{{x}^{3}}+...\] \[=1+ny+\frac{n(n-1)}{2!}{{y}^{2}}+...\] Comparing the terms, we get \[ny\frac{1}{3}x,\frac{n(n-1)}{2!}{{y}^{2}}=\frac{1\times 4}{3\times 6}{{x}^{2}}\] Solving \[n=-1/3,y=-x\]Hence, the given series is \[{{(1-x)}^{-1/3}}\]


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