The answer is the last one because:
- One has three sides and the other has four which doesn't makes it equal.
- One has three vertices and the other has four vertices.
- Obtuse is an angle greater than 90° but less than 180°, so it doesn't have an obtuse angle.
- Yes, it has one right angle each.
The answer would be all of the above
One is called a Newtonian reflector, where a flat mirror is used to point the light rays out to an eye piece.
