Manipal Engineering Manipal Engineering Solved Paper-2009

  • question_answer
    The coefficient of\[{{x}^{24}}\]in the expansion of\[{{(1+{{x}^{2}})}^{12}}(1+{{x}^{12}})(1+{{x}^{24}})\]

    A) \[^{12}{{C}_{6}}\]                                           

    B) \[^{12}{{C}_{6}}+2\]

    C) \[^{12}{{C}_{6}}+4\]      

    D)        \[^{12}{{C}_{6}}+6\]

    Correct Answer: B

    Solution :

    Now,\[{{(1+{{x}^{2}})}^{12}}(1+{{x}^{12}}+{{x}^{24}}+{{x}^{36}})\] \[=[1{{+}^{12}}{{C}_{1}}({{x}^{2}}){{+}^{12}}{{C}_{2}}{{({{x}^{2}})}^{2}}{{+}^{12}}{{C}_{3}}{{({{x}^{2}})}^{3}}\] \[{{+}^{12}}{{C}_{4}}{{({{x}^{2}})}^{4}}{{+}^{12}}{{C}_{5}}{{({{x}^{2}})}^{5}}{{+}^{12}}{{C}_{6}}{{({{x}^{2}})}^{6}}\] \[+...{{+}^{12}}{{C}_{12}}{{({{x}^{2}})}^{12}}]\times (1+{{x}^{12}}+{{x}^{24}}+{{x}^{36}})\] Coefficient of\[{{x}^{24}}{{=}^{12}}{{C}_{6}}{{+}^{12}}{{C}_{12}}+1\] \[{{=}^{12}}{{C}_{6}}+2\]


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