Question 132
Given a positive integer $n$, find the least positive number $\lambda$ such that $\cos \theta_1 + \cos \theta_2 + \cdots + \cos \theta_n$ is not greater than $\lambda$ provided $\tan \theta_1 \cdot \tan \theta_2 \cdot \cdots \cdot \tan \theta_n = 2^{\frac{n}{2}}$ for any $\theta_i \in (0, \frac{\pi}{2})$ ($i=1, 2, \cdots, n$).