12th Class Mathematics Sample Paper Mathematics Olympiad - Sample Paper-1

  • question_answer
    \[\int {{e}^{3\log x{{({{x}^{4}}+1)}^{-1}}dx}}\]is equal to:

    A) \[\frac{1}{4}log\left( {{x}^{4}}+1 \right)+c\]    

    B)  \[log\left( 1+{{x}^{4}} \right)+c\]

    C)  \[-log\left( {{x}^{4}}+1 \right)+c\]       

    D)  \[-\frac{1}{4}log\left( 1+{{x}^{4}} \right)+c\]    

    Correct Answer: A

    Solution :

    [a] \[I={{\int{e}}^{3\log \frac{x}{{{x}^{4}}+1}}}\] \[I={{\int{e}}^{\log \frac{{{x}^{3}}}{1+{{x}^{4}}}}}.dx\] \[I=\int{\frac{{{x}^{3}}}{1+{{x}^{4}}}}.dx\] Let \[z=1+{{x}^{4}}\] \[dz=4{{x}^{3}}dx\] Now \[I=\frac{1}{4}\int{\frac{1}{z}.dz}=\frac{1}{4}.\log z=\frac{1}{4}.\log (1+{{x}^{4}})+c\] Hence, option [a] is correct.


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