RAJASTHAN ­ PET Rajasthan PET Solved Paper-2008

  • question_answer
    The solution of the differential equation\[\left( \frac{dy}{dx} \right)\tan y=\sin (x+y)+\sin (x-y)\]is

    A)  \[sec\text{ }x-1/2\text{ }tan\text{ }y=c\]

    B)  \[log\text{ }sin\text{ (}x+y)=c\]

    C)  \[sec\text{ }x+tan\text{ }y=c\]

    D)  \[sec\text{ }y+2\text{ }cos\text{ }x=c\]

    Correct Answer: D

    Solution :

     Given, differential equation is \[\left( \frac{dy}{dx} \right)\tan y=\sin (x+y)+\sin (x-y)\] \[\Rightarrow \] \[\left( \frac{dy}{dx} \right)\tan y=2\sin x\cos y\] \[\Rightarrow \] \[\frac{\sin y}{{{\cos }^{2}}y}dy=2\sin xdx\] On integrating both sides, we get \[\frac{1}{\cos y}=-2\cos x+c\] \[\Rightarrow \] \[\sec y+2\cos x=c\]


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