CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2001

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

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

    B)         \[\frac{y}{x}\]

    C)  \[y\]                    

    D)         \[x\]

    E)  \[\frac{x}{a}\]

    Correct Answer: B

    Solution :

    \[sec\left( \frac{x+y}{x-y} \right)=a\] \[\Rightarrow \]               \[\left( \frac{x+y}{x-y} \right)={{\sec }^{-1}}(a)\] On differentiating with respect to\[x\] \[\Rightarrow \] \[\frac{(x-y)\left( 1+\frac{dy}{dx} \right)-(x+y)\left( 1-\frac{dy}{dx} \right)}{{{(x-y)}^{2}}}=0\] \[\Rightarrow \] \[x+x\frac{dy}{dx}-y-y\frac{dy}{dx}-x+x\frac{dy}{dx}-y\]                                                                 \[+y\frac{dy}{dx}=0\] \[\Rightarrow \]               \[2x\frac{dy}{dx}=2y\] \[\Rightarrow \]               \[\frac{dy}{dx}=\frac{y}{x}\]


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