Quadrilaterals and Diagonal Lines

Quadrilateral just means “four sides”

A Quadrilateral has four-sides, it is 2-dimensional (a flat shape), closed (the lines join up), and has straight sides.


  • Four sides (edges)
  • Four vertices (corners)
  • The interior angles add up to 360 degrees:

Quadrilateral Angles

Try drawing a quadrilateral, and measure the angles. They should add to 360°

  • A polygon’s diagonals are line segments from one corner to another, but not the sides.

Types of Quadrilaterals

There are special types of quadrilateral:

Types of Quadrilateral

Some types are also included in the definition of other types! For example a square, rhombus and rectangle are also parallelograms.

The Rectangle

Continue reading

Lines of Symmetry

Folding Test

You can find if a shape has a Line of Symmetry by folding it.

When the folded part sits perfectly on top (all edges matching), then the fold line is a Line of Symmetry.


Here I have folded a rectangle one way, and it didn’t work.

symmetry folding no
So this is not a Line of Symmetry

But when I try it this way, it does work (the folded part sits perfectly on top, all edges matching):

symmetry folding yes
So this is a Line of Symmetry


Continue reading