JCECE Engineering JCECE Engineering Solved Paper-2009

  • question_answer
    Solve\[x\cos x\left( \frac{dy}{dx} \right)+y(x\sin x+\cos x)=1\]

    A) \[y=x\tan x+\sin x+c\]

    B) \[x=y\tan x+c\]

    C) \[yx\sec x=\tan x+c\]

    D) \[xy\cos x=x+c\]

    Correct Answer: D

    Solution :

    Given differential equation can be rewritten as                 \[\frac{dy}{dx}+\left( \frac{x\sin x+\cos x}{x\cos x} \right)y=\frac{1}{x\cos x}\] Here,     \[P=\frac{x\sin x+\cos x}{x\cos x}\] \[\therefore \]  \[IF={{e}^{\int{P\,\,dx}}}\]                      \[={{e}^{\int{\frac{x\sin x+\cos x}{x\cos x}dx}}}\]                      \[={{e}^{\log (x\cos x)}}=x\cos x\] \[\therefore \]Solution is                 \[y\cdot x\cos x=\int{\frac{x\cos x}{x\cos x}dx+c}\]                 \[xy\cos x=x+c\]


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