回复：If it is from Ps Q, We can do like that

cma · 2012-01-02 13:48:33Z

回复：If it is from Ps Q, We can do like that简介

来源: cma 于 2012-01-02 13:48:33 [档案] [旧帖] [给我悄悄话] 本文已被阅读：次 (7782 bytes)

回答: If it is from Ps Q, We can do like that 由 jinjing 于 2012-01-02 11:12:38

At each point of reflection, we pretend instead that the light continues to travel straight.Note that after $k$ reflections (excluding the first one at $C$ ) the extended line will form an angle $k \beta$ at point $B$ . For the $k$ th reflection to be just inside or at the point $C$ , we must have $k\beta \le 180 - 2\alpha \Longrightarrow k \le \frac{180 - 2\alpha}{\beta} = 70.27$ . Thus, our answer is, including the first intersection, $\left\lfloor \frac{180 - 2\alpha}{\beta} \right\rfloor + 1 = \boxed{071}$ .