CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2004

  • question_answer
    If \[1+sin\,x+si{{n}^{2}}x+si{{n}^{3}}x+...\,to\,\infty \] \[=4+2\sqrt{3},0<x<\pi ,\]then\[x\]is equal to:

    A)  \[\frac{\pi }{6}\]                                             

    B)  \[\frac{\pi }{4}\]

    C)  \[\frac{3\pi }{4}\]                           

    D)         \[\frac{\pi }{3}or\frac{2\pi }{3}\]

    E)  \[\frac{5\pi }{6}\]

    Correct Answer: D

    Solution :

    \[1+\sin x+{{\sin }^{2}}x+....\infty =4+2\sqrt{3}\] \[\Rightarrow \]               \[\frac{1}{1-\sin x}=4+2\sqrt{3}\] \[\Rightarrow \]               \[1-\sin x=\frac{4-2\sqrt{3}}{4}=1-\frac{2\sqrt{3}}{4}\]   \[\Rightarrow \]               \[\sin x=\frac{\sqrt{3}}{2}=\sin \frac{\pi }{3}\] \[\Rightarrow \]               \[\theta =\frac{\pi }{3}or\frac{2\pi }{3}\]


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