1. Diagonals of quadrilaterals
GM2.2 Extension Plenary
A diagonal of a quadrilateral is a straight line drawn between two opposite vertices. A diagonal line does not have to be inside the quadrilateral.
These coloured lines are diagonals.
Pairs of diagonal lines can have various properties.
They can be equal in length.
They can cut each other in half.
They can cut each other at right angles.
Is this true?
Preamble An activity in which diagonal properties are put forward as a possible alternative means to identify quadrilaterals. Pupils may need reminding of the meaning of “property” and the idea that having it as a means of classification/identifying.
Possible content Properties of quadrilaterals.
Resources Squared/triangle dotted paper to draw (accurately enough to measure) some of the quadrilaterals would be useful.
Solutions/Notes In fact the suggested properties of diagonals do not unambiguously identify all the quadrilaterals – pupils could suggest other properties that would be needed to do this.