যদি $0^{\circ}<\theta<180^{\circ}$, তবে $\sqrt{2+\sqrt{2+\sqrt{\ldots+2(1+\cos \theta)}}}=?$

$2 \cos \frac{0}{2^{n-1}}$

$2 \cos \frac{\theta}{2^{n+1}}$

$2 \cos \frac{\theta}{2^{n}}$

$2 \cos \frac{n \theta}{2}$