CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2010

  • question_answer
    The family of curves\[y={{e}^{a\sin x}},\]where a is an arbitrary constant, is represented by the differential equation

    A)  \[\log y=\tan x\frac{dy}{dx}\]

    B)  \[y\log y=\tan x\frac{dy}{dx}\]

    C)  \[y\log y=\sin x\frac{dy}{dx}\]

    D)  \[\log y=\cos x\frac{dy}{dx}\]

    E)  \[y\log y=\cos x\frac{dy}{dx}\]

    Correct Answer: B

    Solution :

    Given curve is \[y={{e}^{a\sin x}}\]                                       ...(i) Taking log on both sides, we get \[log\text{ }y=a\text{ }sin\text{ }x\]                       ...(ii) Differentiating w.r.t.\[x,\]we get \[\frac{1}{y}\frac{dy}{dx}=a\cos x\]                                    ...(iii) Dividing Eq. (iii) by Eq. (ii), we get                 \[\frac{\frac{1}{y}\frac{dy}{dx}}{\log y}=\frac{a\cos x}{a\sin x}\] \[\Rightarrow \]               \[\frac{dy}{dx}=y\log y\cot x\] \[\Rightarrow \]               \[y\log y=\tan x\frac{dy}{dx}\]


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