Question

$1$$+$ $\cos x$ $+{\cos }^{2}x+\dots .$. to $\infty =4+2\sqrt{3}\Rightarrow x$

• A. ${30}^0$
• B. ${60}^0$
• C. ${45}^0$
• D. ${90}^0$

Answer 1

Answer: (A)

${30}^0$

sum of infinite GP is $\frac{a}{1-r}$
$soLHS=\frac{1}{1-\cos x}=4+2\sqrt{3}$

so we get $\cos x=\frac{\sqrt{3}}{2}$

so $x$ = ${30}^{\circ }$