---
title: "Classifying shapes: cheat sheet"
subtitle: "Angles and shapes"
---

# Classifying shapes

> The words and methods from this unit, with an example of each.

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**triangles by sides and angles**: Give two names: one for the sides (how many are equal) and one for the biggest angle. Equal sides sit opposite equal angles.

$$\text{scalene, isosceles, equilateral} \;\; \text{acute, right-angled, obtuse}$$

_An isosceles acute triangle, its equal sides ticked_

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**quadrilateral family**: Trapezium: at least one pair of parallel sides. Parallelogram: two. Rhombus: four equal sides. Rectangle: four right angles. Square: both. Kite: two pairs of equal neighbouring sides. A square is also a rectangle and a rhombus.

$$\text{every square is a rectangle; every rectangle is a parallelogram}$$

_A square with equal sides, parallel sides and right angles marked_

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**regular polygon**: Both are needed: a rhombus has equal sides but is not regular. Names: pentagon 5, hexagon 6, heptagon 7, octagon 8, nonagon 9, decagon 10.

$$\text{equal sides} \;\text{and}\; \text{equal angles}$$

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**convex and concave**: Convex: every corner points out. Concave: at least one corner points in.

$$\text{concave: an angle} > 180^\circ$$

_A concave hexagon with one corner pointing in_

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