what is the gradient of the line so that when a ball bounces (perfectly elastically of course) twice it then hits the mid-point of the lower side of the square?
some variety of techniques can be used and it doesn't involve higher mathematical techniques
- trigonometry isn't needed
- it can be helpful to have some previous consideration about what happens to the gradient of a line when it is reflected
- or some consideration of when triangles are similar
- or you could solve this, very neatly, by working with the 'principle of reflections'
students could also consider the length of the path(s)