JEE Main & Advanced Mathematics Binomial Theorem and Mathematical Induction Question Bank Critical Thinking

  • question_answer
    If the sum of the coefficients in the expansion of \[{{(1-3x+10{{x}^{2}})}^{n}}\] is a and if the sum of the coefficients in the expansion of  \[{{(1+{{x}^{2}})}^{n}}\] is b, then [UPSEAT 2001]

    A) \[a=3b\]

    B) \[a={{b}^{3}}\]

    C) \[b={{a}^{3}}\]

    D) None of these

    Correct Answer: B

    Solution :

    We have a = sum of the coefficient in the expansion of \[{{(1-3x+10{{x}^{2}})}^{n}}={{(1-3+10)}^{n}}={{(8)}^{n}}\]        Þ \[{{(1-3x+10{{x}^{2}})}^{n}}={{(2)}^{3n}}\],  [Putting x = 1] . Now, b = sum of the coefficients in the expansion of \[{{(1+{{x}^{2}})}^{n}}={{(1+1)}^{n}}={{2}^{n}}\]. Clearly, \[a={{b}^{3}}\]


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