Formation of a triangle

Three lines intersect with each other in a plane to form a closed figure. Vertices are formed at the intersecting points and edges that mark the triangle are sides.

Objectives

 * Understand formation of triangles
 * Recognize elements of triangle
 * Introduce concepts of exterior angle.

Estimated Time
30 minutes

Prerequisites/Instructions, prior preparations, if any
Prior knowledge of point, lines, angles, parallel lines

Materials/ Resources needed

 * Digital : Computer, geogebra application, projector.
 * Non digital : Worksheet and pencil
 * Geogebra files : “Introduction to a triangle.ggb”

Process (How to do the activity)
Evaluation at the end of the activity
 * Use the geogebra file to illustrate.
 * How many lines are there? Are the lines meeting?
 * Are the two lines parallel? How can you say they are parallel or not?
 * How many angles are formed at the point of intersection?
 * What is the measure of the total angle at the point of intersection of two lines?
 * Of the four angles formed which of the angles are equal? What are they called?
 * Do the three intersecting lines enclose a space? How does it look? It is called a triangle.
 * What are the points of intersection of these three lines called?
 * The line segments forming the triangle are called sides.
 * How many angles are formed when three lines intersect with each other?
 * How many angles are enclosed by the triangle?
 * Can there be a closed figure with less than three sides?
 * Can the vertices of the triangle be anywhere on a plane?
 * What will happen if the three vertices are collinear?