2. Rectangle: A parallelogram with right angles is a rectangle. A rectangle is a special parallelogram, and a square is a special rectangle.
3. Diagonal: A geometric term defined as a line segment connecting any two nonadjacent vertices of a polygon or a line segment connecting any two vertices of a polyhedron that are not on the same plane. In addition, in algebra, n-order determinant, the numbers from upper left to lower right belong to the main diagonal, and the numbers from upper left to upper right belong to the sub-diagonal. The word "diagonal" comes from the relationship between "angle" and "angle" in ancient Greek.