JEE Main & Advanced JEE Main Paper (Held On 26 May 2012)

  • question_answer
    If [x] is the greatest integer \[\le x,\] then the value of the integral\[\int\limits_{-0.9}^{0.9}{\left( \left[ {{x}^{2}} \right]+\log \left( \frac{2-x}{2+x} \right) \right)dx}\]is.   JEE Main Online Paper (Held On 26-May-2012)  

    A) 0.486                                    

    B)                         0.243

    C)                         1.8                                        

    D)                         0

    Correct Answer: D

    Solution :

                    \[\int\limits_{-0.9}^{0.9}{\left\{ [{{x}^{2}}]+\log \left( \frac{2-x}{2+x} \right) \right\}dx}\] \[=\int\limits_{-0.9}^{0.9}{\left\{ [{{x}^{2}}]dx+\int\limits_{-0.9}^{0.9}{\log }\left( \frac{2-x}{2+x} \right) \right\}dx}\] \[=0+\int\limits_{-0.9}^{0.9}{\log \left( \frac{2-x}{2+x} \right)dx}\] Put\[x=-x\Rightarrow f(x)=\log \frac{2-x}{2+x}\] and\[f(-x)=\log \frac{2+x}{2-x}\] \[=-\log \frac{(2+x)}{2-x}=-f(x)\] So, it is an odd function, hence Required integral 1 = 0.


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