Classify Polygons
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What you will learn
- 1Identify and name common polygons
- 2Sort polygons by number of sides and angles
- 3Describe properties that distinguish triangles, quadrilaterals, and other polygons
Mini Lesson
A polygon is a closed flat shape with straight sides. Every polygon has as many angles as it has sides. We name and classify polygons by counting their sides.
Triangles
- A triangle has 3 sides and 3 angles.
- Types include equilateral (all sides equal), isosceles (two sides equal), scalene (no sides equal), and right triangle (one 90° angle).
- The three angles of any triangle always add up to 180°.
Quadrilaterals
- A quadrilateral has 4 sides and 4 angles.
- Examples: square (4 equal sides, 4 right angles), rectangle (opposite sides equal, 4 right angles), rhombus (4 equal sides, opposite angles equal), trapezoid (one pair of parallel sides).
- The four angles of any quadrilateral always add up to 360°.
Other Polygons
- Pentagon: 5 sides, 5 angles.
- Hexagon: 6 sides, 6 angles (like a honeycomb cell).
- Octagon: 8 sides, 8 angles (like a stop sign).
- A regular polygon has all sides equal and all angles equal.
Words to know
Polygon
A flat, closed shape with three or more straight sides
e.g. A triangle is a polygon.
Quadrilateral
A polygon with exactly 4 sides
e.g. A square is a quadrilateral.
Regular polygon
A polygon with all sides equal and all angles equal
e.g. A regular hexagon has six equal sides.
Vertex
A corner where two sides of a polygon meet
e.g. A pentagon has 5 vertices.
Side
A straight edge of a polygon
e.g. An octagon has 8 sides.
Tip: count the sides to name the polygon — tri = 3, quad = 4, penta = 5, hexa = 6, octa = 8. Every polygon has the same number of sides, angles, and vertices.
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