JCECE Engineering JCECE Engineering Solved Paper-2014

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

    A) \[144\]                                 

    B) \[288\]

    C) \[216\]                                 

    D)  \[576\]

    Correct Answer: D

    Solution :

    \[{{(1+3x+2{{x}^{2}})}^{6}}={{\{1+x(3+2x)\}}^{6}}\] \[=1{{+}^{6}}{{C}_{1}}\times (3+2x){{+}^{6}}{{C}_{2}}{{x}^{2}}{{(3+2x)}^{2}}\]\[{{+}^{6}}{{C}_{3}}{{x}^{3}}{{(3+2x)}^{3}}{{+}^{6}}{{C}_{4}}{{x}^{4}}{{(3+2x)}^{4}}\]\[{{+}^{6}}{{C}_{5}}x{{(3+2x)}^{5}}{{+}^{6}}{{C}_{6}}{{x}^{6}}{{(3+2x)}^{6}}\] Only \[{{x}^{11}}\] gets form\[^{6}{{C}_{6}}{{x}^{6}}{{(3+2x)}^{6}}\] \[\because \]     \[^{6}{{C}_{6}}{{x}^{6}}{{(3+2x)}^{6}}={{x}^{6}}{{(3+2x)}^{6}}\] \[\therefore \]  Coefficient of\[{{x}^{11}}{{=}^{6}}{{C}_{5}}3\cdot {{2}^{5}}=576\]


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