CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2001

  • question_answer
    If\[y=x\text{ }tan\text{ }y,\]then\[\frac{dy}{dx}\]is equal to:

    A)  \[\frac{\tan y}{x-{{x}^{2}}-{{y}^{2}}}\]                  

    B)  \[\frac{y}{x-{{x}^{2}}-{{y}^{2}}}\]

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

    D)  \[\frac{\tan x}{x-{{y}^{2}}}\]

    E)  \[\frac{\tan y}{x+{{x}^{2}}+{{y}^{2}}}\]

    Correct Answer: B

    Solution :

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


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