CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2007

  • question_answer
    lf\[\sec \left( \frac{x-y}{x+y} \right)=a,\]then\[\frac{dy}{dx}\]is

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

    B)  \[-\frac{y}{x}\]

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

    D)         \[-\frac{x}{y}\]

    E)  \[\frac{x-y}{x+y}\]

    Correct Answer: A

    Solution :

    \[\because \]\[\sec \left( \frac{x-y}{x+y} \right)=a\] \[\Rightarrow \]               \[\frac{x-y}{x+y}={{\sec }^{-1}}a\] On differentiating w.r.t.\[x,\]we get \[\frac{(x+y)\left( 1-\frac{dy}{dx} \right)-(x-y)\left( 1+\frac{dy}{dx} \right)}{{{(x+y)}^{2}}}=0\] \[\Rightarrow \] \[x+y-x+y-\{x+y+x-y\}\frac{dy}{dx}=0\] \[\Rightarrow \] \[2y=2x\frac{dy}{dx}\Rightarrow \frac{dy}{dx}=\frac{y}{x}\]


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