BCECE Engineering BCECE Engineering Solved Paper-2002

  • question_answer
    The value of coefficient which is independent  from \[x\] in\[{{\left( 2x-\frac{3}{{{x}^{2}}} \right)}^{6}},\]is :

    A) \[~-\,2916\]                                       

    B)  4860     

    C)         2160                     

    D)         none of these

    Correct Answer: C

    Solution :

    The general term in the expansion of\[{{\left( 2x-\frac{3}{{{x}^{2}}} \right)}^{6}}\]is \[{{T}_{r+1}}={{\,}^{6}}{{C}_{r}}{{(2x)}^{6-r}}{{\left( -\frac{3}{{{x}^{2}}} \right)}^{r}}\] \[={{(-1)}^{r}}{{\,}^{6}}{{C}_{r}}{{2}^{6-r}}{{.3}^{r}}{{x}^{6-3r}}\] \[\therefore \]The term independent of \[x,\] if \[6-3r=0\]\[\Rightarrow \]           \[r=2\] \[\therefore \]\[{{T}_{3}}={{\,}^{6}}{{C}_{2}}{{.2}^{4}}{{.3}^{2}}=2160\]


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