Supplementary angles

From Karnataka Open Educational Resources

Supplementary angles are two angles with a sum of 180°. A common case is when they lie on the same side of a straight line.


Introduce children to concept of supplementary angles

Estimated Time

30 minutes

Prerequisites/Instructions, prior preparations, if any

Prior knowledge of point, lines, angles

Materials/ Resources needed

  • 1. Digital : Computer, geogebra application, projector.
  • 2. Non digital : Worksheet and pencil.
  • 3. Geogebra files : Supplementary angles.ggb

Download this geogebra file from this link.

Process (How to do the activity)

  • Prior hands on activity (optional – children can use news paper strips to make angles and place them together and notice if the resulting angle formed is a straight angle).
  • Students should be able to identify the types of angles in the file
  • Let them attempt to join the two angle - They may try by coinciding different points or lines.
  • Ask about the angle formed by joining the two angles
  • Is the straight angle formed parallel to the x-axis.
  • Challenge them to find another way to make a straight angle using the two existing angles.
  • Interchanging the position of the two angles – ask what they notice.
  • If one of the angle is changed will the two together again form supplementary angle.
  • Readjust to make adjacent angles again to notice the resultant angle.
  • Children can be asked to make note of the angle measures for different positions of the slider in the work sheet
  • Ask students if the angles have to be adjacent to be supplementary pairs.
  • Record the values of the two angles and their sum in the worksheet
Sl No. Value of slider α Angle ABC Angle DEF Sum

Angle ABC + Angle DEF

Is angle ABC supplement of angle DEF
  • Evaluation at the end of the activity
  1. What are supplementary pair of angles?
  2. Is it required for the pair of angles to be adjacent to be supplementary?
  3. What type of angles form supplementary pair?