Two dimensional shapes have specific names and properties that describe their sides, angles and symmetry. Knowing this vocabulary allows shapes to be identified, compared and described accurately.

 

 

Triangles

A triangle is a polygon with three sides and three angles.

 

• A scalene triangle has all sides and angles different
• An isosceles triangle has two sides equal and two angles equal
• An equilateral triangle has all sides equal and all angles equal
• A right angled triangle has one angle equal to a right angle

 

Triangles always have interior angles that add up to a straight angle.

 

 

 

Quadrilaterals

A quadrilateral is a polygon with four sides.

 

• A square has four equal sides and four right angles
• A rectangle has opposite sides equal and four right angles
• A parallelogram has opposite sides equal and parallel (opposite side-pair 1 may have different lengths to opposite side-pair 2)
• A rhombus has four equal sides but angles are not necessarily right angles 
• A kite has two pairs of adjacent equal sides
• A trapezium has one pair of parallel sides

 

Different quadrilaterals share properties, but each has defining features that make it unique.

 

 

 

Polygons

A polygon is a closed shape made from straight line segments.

 

Examples include:
• pentagon with five sides
• hexagon with six sides
• octagon with eight sides

 

A regular polygon has all sides equal and all angles equal.

 

An irregular polygon does not have all sides and angles equal.

 

 

 

Circles

A circle is a curved shape where every point on the edge is the same distance from the centre.

 

Important circle vocabulary includes:

• radius which is the distance from the centre to the edge
• diameter which is twice the radius and passes through the centre
• circumference which is the distance around the circle
• tangent which is a straight line that touches the circle at exactly one point
• chord which is a straight line joining two points on the circumference
• arc which is part of the circumference
• sector which is a region formed by two radii and an arc
• segment which is a region between a chord and an arc

 

Each part describes a different feature of the circle.

 

 

 

Key Points to Remember

Two dimensional shapes are classified by sides and angles.
Triangles and quadrilaterals have distinct named types.
Polygons are closed shapes with straight sides.
Regular shapes have equal sides and angles.
Circles have specific parts with precise definitions.

 

Using correct vocabulary and understanding properties allows you to identify and describe 2-D shapes clearly and confidently.