Answer
This is a writing exercise for the student, and answers will vary.
Work Step by Step
Sample:
Hi Grandma! I texted you a drawing that I made. It shows that a mirror which is just half your height is enough to show your entire body, if it is placed at the correct distance from the floor. As you can see from the diagram, it doesn't even matter how far away the mirror is.
If you move closer to the plane of the mirror, your image moves closer too. Try it and see! The formal proof depends on the law of reflection.
If the mirror is mounted too high or low, it'll need to be a little longer, but a half-height mirror is sufficient when it is properly mounted.
