JEE Main & Advanced Mathematics Binomial Theorem and Mathematical Induction Question Bank General term, Coefficient of any power of x, Independent term, Middle term and Greatest term and Greatest coefficient

  • question_answer
    In the expansion of \[{{(1+3x+2{{x}^{2}})}^{6}}\]the coefficient of \[{{x}^{11}}\] is  [Kerala (Engg.) 2005]

    A)   144

    B) 288

    C) 216

    D) 576

    E) (3)(211)

    Correct Answer: D

    Solution :

    \[{{(1+3x+2{{x}^{2}})}^{6}}\] = \[{{[1+x(3+2x)]}^{6}}\]                         = \[1+{{\,}^{6}}{{C}_{1}}x(3+2x){{+}^{6}}{{C}_{2}}{{x}^{2}}{{(3+2x)}^{2}}\]\[{{+}^{6}}{{C}_{3}}{{x}^{3}}{{(3+2x)}^{3}}{{+}^{6}}{{C}_{4}}{{x}^{4}}{{(3+2x)}^{4}}\]\[{{+}^{6}}{{C}_{5}}{{x}^{5}}{{(3+2x)}^{5}}{{+}^{6}}{{C}_{6}}{{x}^{6}}{{(3+2x)}^{6}}\] Only \[{{x}^{11}}\] gets from \[^{6}{{C}_{6}}{{x}^{6}}{{(3+2x)}^{6}}\] \[\because \]  \[^{6}{{C}_{6}}{{x}^{6}}{{(3+2x)}^{6}}=\,{{x}^{6}}{{(3+2x)}^{6}}\] \[\therefore \] Coefficient of \[{{x}^{11}}\] = \[^{6}{{C}_{5}}{{3.2}^{5}}=576\].


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