Let's list all information we have:
- quadrilateral (4 sides)
- opposite sides congruent and parallel.
- all angles are 90°
- diagonal are congruent.
So, if we have a quadrilateral, we have something like this:
However, it is given that all anlges are 90°, which limits our possible drawing. So, something like this:
Let's see, this is a rectangle, it has opposite side congruent (equal length), the opposite sides are parallel, all the angles are 90° and the Diagonals have equal lengths, because they form congruent triangles.
It could also be a square:
Beucase it has all of the characteristics given.
