JEE Main & Advanced Mathematics Binomial Theorem and Mathematical Induction Question Bank Expansion of binomial theorem

  • question_answer
    If \[{{T}_{0}},{{T}_{1}},{{T}_{2}},....{{T}_{n}}\] represent the terms in the expansion of \[{{(x+a)}^{n}}\], then \[{{({{T}_{0}}-{{T}_{2}}+{{T}_{4}}-....)}^{2}}\] \[+{{({{T}_{1}}-{{T}_{3}}+{{T}_{5}}-....)}^{2}}=\]

    A) \[({{x}^{2}}+{{a}^{2}})\]

    B) \[{{({{x}^{2}}+{{a}^{2}})}^{n}}\]

    C) \[{{({{x}^{2}}+{{a}^{2}})}^{1/n}}\]

    D)   \[{{({{x}^{2}}+{{a}^{2}})}^{-1/n}}\]

    Correct Answer: B

    Solution :

    From the given condition, replacing a by ai and ? ai respectively, we get \[{{(x+ai)}^{n}}=({{T}_{0}}-{{T}_{2}}+{{T}_{4}}-....)+i({{T}_{1}}-{{T}_{3}}+{{T}_{5}}-....)\]  ....(i) and \[{{(x-ai)}^{n}}=({{T}_{0}}-{{T}_{2}}+{{T}_{4}}-....)-i({{T}_{1}}-{{T}_{3}}+{{T}_{5}}-....)\]  ......(ii) Multiplying (ii) and (i) we get required result    i.e.  \[{{({{x}^{2}}+{{a}^{2}})}^{n}}={{({{T}_{0}}-{{T}_{2}}+{{T}_{4}}-....)}^{2}}+{{({{T}_{1}}-{{T}_{3}}+{{T}_{5}}-....)}^{2}}\]


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