JEE Main & Advanced JEE Main Paper (Held On 16 April 2018)

  • question_answer
    If \[x=\sqrt{{{2}^{\cos e{{c}^{-1}}t}}}\]and \[y=\sqrt{{{2}^{{{\sec }^{-1t}}}}(|t|\ge 1)},\]then \[\frac{dy}{dx}\]is equal to.    [JEE Main 16-4-2018]

    A)  \[\frac{y}{x}\]                                   

    B) \[-\frac{y}{x}\]

    C)  \[-\frac{x}{y}\]                                  

    D)  \[\frac{x}{y}\]

    Correct Answer: B

    Solution :

     \[\frac{dx}{dt}=\frac{1}{2\sqrt{{{2}^{\cos e{{c}^{-1}}t}}}}\]\[{{2}^{^{\cos e{{c}^{-1t}}}}}\log 2.\frac{-1}{x\sqrt{{{x}^{2}}-1}}\]                 \[\frac{dy}{dt}=\frac{1}{2\sqrt{{{2}^{{{\sec }^{-1t}}}}}}{{2}^{{{\sec }^{-1t}}}}\log 2.\frac{1}{x\sqrt{{{x}^{2}}-1}}\]                 Thus \[\frac{dy}{dx}=\frac{\frac{dy}{dt}}{\frac{dx}{dt}}=\frac{-\sqrt{{{2}^{{{\operatorname{cosec}}^{-1}}t}}}}{\sqrt{{{2}^{{{\sec }^{-1t}}}}}}\frac{{{2}^{{{\sec }^{-1}}t}}}{{{2}^{\cos e{{c}^{-1}}t}}}\] \[\frac{dy}{dx}=\frac{\frac{dy}{dt}}{\frac{dx}{dt}}=\sqrt{\frac{{{2}^{{{\sec }^{-1}}t}}}{{{2}^{\cos e{{c}^{-1}}t}}}}=\frac{-y}{x}\]


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