JCECE Engineering JCECE Engineering Solved Paper-2008

  • question_answer
    In the expansion of\[{{\left( 2{{x}^{2}}-\frac{1}{x} \right)}^{12}}\], the term independent of \[x\] is

    A) \[8th\]                                 

    B) \[7th\]

    C) \[9th\]                                 

    D) \[10th\]

    Correct Answer: C

    Solution :

    The general term in the expansion of\[{{\left( 2{{x}^{2}}-\frac{1}{x} \right)}^{12}}\]is                 \[{{T}_{r+1}}{{=}^{12}}{{C}_{r}}{{(2{{x}^{2}})}^{12-r}}\cdot {{\left( -\frac{1}{x} \right)}^{r}}\]                 \[={{(-1)}^{r}}^{12}{{C}_{r}}{{2}^{12-r}}\cdot {{x}^{24-2r-r}}\]                 \[={{(-1)}^{r}}^{12}{{C}_{r}}\cdot {{2}^{12-r}}\cdot {{x}^{24-3r}}\] The term independent of\[x\], if                 \[24-3r=0\] \[\Rightarrow \]               \[24=3r\] \[\Rightarrow \]               \[r=8\] Now,     \[r+1=8+1\]                 \[=9th\]term


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