2D Shapes

A shape is a geometrical figure like a square, circle or kite.

A 2 dimensional (2D) shape is drawn on the surface of a plane, in 2 dimensions only.

(A plane is like a piece of paper)

Triangles

• A triangle is a polygon with 3 sides.

• There are three types of triangle; scalene, isosceles and equilateral.

• A triangle can also be called a trigon.

• The only regular triangle is the equilateral triangle.

Quadrilaterals

• A quadrilateral is a polygon with 4 sides.

• There are seven common types of quadrilateral; square, rectangle, rhombus, parallelogram, trapezium, kite & arrowhead.

• A quadrilateral can also be called a tetragon.

• The only regular quadrilateral is the square.

2D shapes with more than 4 sides are given prefixes (eg hex, sept, oct) alongside the word gon (meaning sides).

If all sides and interior angles are the same size, it is a regular polygon, otherwise, it is an irregular polygon.

After 8 sides, we use the following prefixes;

9 sides = nonagon

10 sides = decagon

11 sides = undecagon

12 sides = dodecagon

A circle is a two dimensional (2D) shape.

It is defined as a set of points that are all the same distance away from a point called the centre.

Some people say that a circle is a polygon with an infinite amount of sides.

A semicircle is half of a circle.