Quadrilaterals (Properties)

Quadrilaterals, like triangles, appear just about everywhere, and so it is important to have a good understanding of their properties. Starting at a very general level, the sum of the interior angles will add up to 360^o. Can you remember why this is so? Draw in a diagonal, and it will form 2 triangles. The sum of the angles in a triangle is 180^o, so the sum of two triangles will be 360^o.

Once you start adding on other properties, such as a pair of parallel sides, opposite sides are equal length, diagonals bisect each other, then you create special quadrilaterals, that each have their own name.

You will need to know what makes a rhombus, what is special about a trapezium, or a parallelogram (think parallel bars in gymnastics), or a kite.

We often think of a square as a special case of a rectangle – they both have 4 right-angles, a rectangle has 2 pairs of equal sides while a square has all sides equal. But a square could also be considered as a special case of a rhombus – a rhombus is a parallelogram with all sides equal, and a square is a rhombus with all angles equal.

Quadrilaterals whose diagonals intersect at 90^o are particularly important when it comes to Pythagoras and Trigonometry, can you work out why?