This diagram shows that Al can see the reflections of Ed and Fred in the mirror. Which two students can both see the reflections of Cy, Di, Ed and Fred? *

  Cy and Di

Explanation:

We cannot tell exactly where the right end of the mirror is, but if we assume it is short of allowing Ed and Fred to see each other, we have the following:

  Cy can see Cy and everyone to the right

  Fred can see Di and everyone to the left

The only two that can see all of Cy, Di, Ed, and Fred are Cy and Di.

_____

If the mirror extends far enough to the right for Ed to see Fred, then all of Cy, Di, and Ed can see the four folks of interest.

pecialized keyboards

the components of a vector are the parts of the vectors that are to each other.

b perpendicular