BCECE Engineering BCECE Engineering Solved Paper-2012

  • question_answer
    If \[1+\sin x+{{\sin }^{2}}x+\]upto \[\infty \] \[=4+2\sqrt{3},0<x<\pi \]and \[x\ne \frac{\pi }{2},\]then \[x\]is equal to

    A)  \[\frac{\pi }{3},\frac{5\pi }{6}\]                

    B)  \[\frac{2\pi }{3},\frac{\pi }{6}\]

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

    D)         \[\frac{\pi }{6},\frac{\pi }{3}\]

    Correct Answer: C

    Solution :

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


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