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8. Sequences and Series
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If $1\, + \,\sin x\, + \,{\sin ^2}x\, + \,...\infty \, = \,4\, + \,2\sqrt 3 ,\,0\, < \,x\, < \,\pi $ then
A
$x = \frac{\pi }{6}$
B
$x = \frac{\pi }{3}$
C
$x = \frac{\pi }{6}$ or $\frac{\pi }{3}$
D
none of these
Solution
$1+\sin x+\sin ^{2} x \ldots \ldots \ldots=4+2 \sqrt{3}$
$\Rightarrow \frac{1}{1-\sin x}=4+2 \sqrt{3}$
$\Rightarrow \sin x=-\frac{\sqrt{3}}{2}$
$\Rightarrow$ No value of $x$ in $(0, \pi)$
Standard 11
Mathematics