Grade 5 · Math · Lesson 26

Triangles and Polygons

A polygon is a closed flat shape made only of straight line segments. Polygons are named by how many sides they have. The number of sides always matches the number of vertices (corners). Triangles are the simplest polygon family, and they get extra names based on their sides and their angles.

What this lesson teaches

1Identify polygons by counting sides and vertices
2Name common polygons including triangle, quadrilateral, pentagon, and hexagon
3Classify triangles by their sides as equilateral, isosceles, or scalene
4Classify triangles by their angles as right, acute, or obtuse

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