JCECE Engineering JCECE Engineering Solved Paper-2003

  • question_answer
    6th term in expansion of\[{{\left( 2{{x}^{2}}-\frac{1}{3{{x}^{2}}} \right)}^{10}}\]is:

    A) \[\frac{4580}{17}\]                         

    B) \[-\frac{896}{27}\]

    C) \[\frac{5580}{17}\]                         

    D)   none of these

    Correct Answer: B

    Solution :

    Key Idea : The general term in the expansion of \[{{(x+a)}^{n}}\]is                 \[{{T}_{r+1}}{{=}^{n}}{{C}_{r}}{{x}^{n-r}}{{d}^{r}}\] Given expansion is\[{{\left( 2{{x}^{2}}-\frac{1}{3{{x}^{2}}} \right)}^{10}}\] \[\therefore \]  \[{{T}_{r+1}}{{=}^{10}}{{C}_{r}}{{(2{{x}^{2}})}^{10-r}}{{\left( -\frac{1}{3{{x}^{2}}} \right)}^{r}}\] \[\Rightarrow \]               \[{{T}_{6}}{{=}^{10}}{{C}_{5}}{{(2{{x}^{2}})}^{5}}{{\left( -\frac{1}{3{{x}^{2}}} \right)}^{5}}\]                 \[=-\frac{10!\times 32}{5!5!}\times \frac{1}{243}\]                 \[=-\frac{896}{27}\]


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