CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2001

  • question_answer
    \[\frac{d}{dx}\left[ {{\tan }^{-1}}\left( \frac{a-x}{1+ax} \right) \right]\]is equal to:

    A) \[-\frac{1}{1+{{x}^{2}}}\]                             

    B) \[\frac{1}{1+{{a}^{2}}}-\frac{1}{1+{{x}^{2}}}\]

    C)  \[\frac{1}{1+{{\left( \frac{a-x}{1+ax} \right)}^{2}}}\]      

    D)  none of these

    Correct Answer: A

    Solution :

    \[y={{\tan }^{-1}}\left( \frac{a-x}{1+ax} \right)\]put \[a=\tan \theta ,\]\[x=\tan \text{o }\!\!|\!\!\text{ }\] \[y={{\tan }^{-1}}\left( \frac{\tan \theta -\tan \text{o }\!\!|\!\!\text{ }}{1+\tan \theta \operatorname{tano}|} \right)\]                 \[\Rightarrow \]               \[y={{\tan }^{-1}}\tan (\theta -o|)\]                 \[y={{\tan }^{-1}}a-{{\tan }^{-1}}x\Rightarrow \frac{dy}{dx}=-\frac{1}{1+{{x}^{2}}}\]


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