A line segment joining two nonadjacent vertices of a polygon.
In geometry, a diagonal is a straight line that connects two corners (or vertices) of a shape, but not ones that are next to each other. This line goes across the shape, skipping at least one side.
For example:
- In a square or rectangle, connecting opposite corners forms a diagonal.
- In polygons with more than four sides, like a pentagon, multiple diagonals can be drawn by connecting nonadjacent vertices.
Diagonals help us understand and break down shapes, especially when we’re learning about angles, symmetry, or area.
We see diagonals in real life in things like:
- Kites and paper folds
- Designs on quilts or tiles
- Cross braces in bridges and buildings
When Do Students Learn About Diagonals?
Students start learning about diagonals when they study shapes more closely and work with their properties.
Grades 3–5 – Identifying and Drawing Diagonals
Students recognize diagonals in polygons and use them to explore shape properties like symmetry and angle measures.
