Sum of the interior angles of a quadrilateral

The sum of the measures of the angles in any quadrilateral is 4 right angles.

Objectives
To establish that sum of interior angles of any quadrilateral is 360°

Estimated Time
40 minutes

Prerequisites/Instructions, prior preparations, if any
Prior knowledge of point, lines, angles, intersecting lines, vertically opposite angles, properties of triangle

Materials/ Resources needed

 * Digital: Computer, geogebra application, projector.
 * Non digital : Worksheet and pencil
 * Geogebra files : ‘Sum of the interior angles of a quadrilateral.ggb’

Process (How to do the activity)

 * In the geogebra sketch for the quadrilateral measure the sides and angles at the vertices
 * Calculate the sum of these angles of the quadrilateral? Note your observations
 * Draw any one diagonal. What do you notice? What is the quadrilateral divided into? How many triangles are formed?
 * What is the measure of the sum of angles in each quadrilateral? So what is the measure of all the angles of the quadrilateral?
 * Make different quadrilaterals. Divide it into two triangles, measure the angles of the two triangles, check their sum.
 * Tabulate the angles of the two triangles

Evaluation at the end of the activity
 * Is the sum of all angles in any quadrilateral 360o.