Ex2a: Reflection in the line y = 0
What stays the same and what changes as you move the points around?
Are there any points that do not move under this transformation?
Where would the co-ordinate (x,y) map to?
随着点的移动，什么保持不变，什么改变？
在此转换过程中，有没有要解决的问题？
坐标（x，y）会映射到哪里？
Created by N.Trubridge