下面的几道有关反射现象的几何光学题 ,不但有趣 ,同时还蕴含着比较深刻的数学哲理 .1　“沿原路返回”的条件题目 :如图 1所示 ,两平面镜 M1、M2 的夹角为θ.过 P点有一条与 M1成α角的方向射向 Q点的光线 .要使该光线经两面镜若干次反射后能沿原路返回 ,试推导α、θ应满足的 The following few geometric optical problems concerning reflections are not only interesting but also contain a deeper philosophy of mathematics. 1 “Back along the original road” conditions Title: As shown in Figure 1, the angle between the two plane mirrors M1 and M2 For θ. P points have a ray that strikes Q point in the direction of angle α from M1. To allow the light to return along the original path after several reflections by the two mirrors, try to derive that α, θ should satisfy