Manipal Engineering Manipal Engineering Solved Paper-2009

  • question_answer
    The eccentricity of the conic\[\frac{5}{r}=2+3\cos \theta +4\sin \theta \]is

    A) \[\frac{1}{2}\]                                   

    B) \[1\]

    C) \[\frac{3}{2}\]                   

    D)        \[\frac{5}{2}\]

    Correct Answer: D

    Solution :

    Given,\[\frac{5}{r}=2+3\cos \theta +4\sin \theta \] \[\Rightarrow \]               \[\frac{5}{r}=2+5\left( \frac{3}{5}\cos \theta +\frac{4}{5}\sin \theta  \right)\] \[\Rightarrow \]               \[\frac{5/2}{r}=1+\frac{5}{2}(\cos \phi \cos \theta +\sin \phi \sin \theta )\]                 \[\left( \text{put}\,\,\cos \phi =\frac{3}{5},\,\,\text{then}\,\,\sin \phi =\frac{4}{5} \right)\] \[\Rightarrow \]               \[\frac{5/2}{r}=1+\frac{5}{2}\cos (\theta -\phi )\] It is of the form\[\frac{l}{r}=1+e\cos \theta \] \[\therefore \]  \[e=\frac{5}{2}\]


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