Angle between diagonals α:
- A rectangle has opposite sides equal and parallel
- The sides of the rectangle are its heights
- The diagonals of the rectangle are equal, intersect, and the intersection is halved.
- The square of the diagonal of a rectangle is equal to the sum of the squares of its two adjacent sides (by the Pythagorean theorem)
- The rectangle is a parallelogram, its opposite sides are pairwise parallel
- A circle can be described around any rectangle, and the diagonal of the rectangle is equal to the diameter of the circumscribed circle, the radius is equal to the half-diagonal.