Comparing and classifying shapes
In a nutshell
2D shapes, sometimes known as plane shapes, are flat and all have different properties. It is important to be able to classify them based on their properties.
Properties
A property is a quality that a shape has. Below is a list that highlights the key properties of shapes:
- Number of sides.
- Number of angles or corners.
- Length of sides.
- Types of angles (acute, obtuse, reflex or right-angle).
- Parallel and perpendicular lines.
Triangles
All triangles have three sides and three angles. However, different triangles have different properties depending on how they are drawn. A triangle could be:
- Equilateral - all three sides are the same and all three angles are the same.
- Isosceles - two sides and two angles are the same.
- Scalene - all sides and angles are different.
- Right-angled - one angle is 90 degrees (a right angle).
It is important to look carefully at the triangle and its properties in order to classify it correctly.
Quadrilaterals
A quadrilateral is a shape with four sides and four angles. Here are a few examples of quadrilaterals and their properties:
sHAPE | pROPERTIES | dIAGRAM |
Rectangle | - Two pairs of equal sides.
- Angles all right angles (perpendicular lines).
- Two pairs of parallel lines.
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Square | - A special case of a rectangle.
- Sides all equal in length.
- Angles all right angles (perpendicular lines).
- Two pairs of parallel lines.
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Trapezium | - One pair of parallel lines.
- Two sets of equal angles.
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Kite | - Two pairs of equal sides.
- One pair of equal angles.
- No parallel lines.
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Regular polygons
A regular polygon is a shape that has all equal sides and equal angles. Here are some examples of the most common regular polygons and their properties:
Shape | Properties | Diagram |
Pentagon | - Five equal sides and angles.
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Hexagon | - Six equal sides and angles.
- Three pairs of parallel lines.
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Heptagon | - Seven equal sides and angles.
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Octagon | - Eight equal sides and angles.
- Four pairs of parallel lines.
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Irregular polygons
Irregular polygons are shapes that have sides and angles of different sizes. The left image below is a regular pentagon. The right image below is an irregular pentagon.
Tip: You can always identify a polygon by how many sides it has. For example, a pentagon is always a shape that has five sides, regardless of whether it is regular or irregular.