$\cos \theta=\frac{1}{2}\left(x+\frac{1}{x}\right)$ হলে, $\cos 2 \theta=$ কত?

$\left(x+\frac{1}{x}\right)^{2}$

$\frac{1}{2}\left(x^{2}+\frac{1}{x^{2}}\right)$

$2\left(x^{2}+\frac{1}{x^{2}}\right)$

$\left(x-\frac{1}{x}\right)^{2}$