# Complementary angles

From Karnataka Open Educational Resources

Complementary angles are two angles with a sum of 90°. A common case is when they form a right angle.

### Objectives

Introduce children to concept of complementary angles

### Estimated Time

30 minutes

### Prerequisites/Instructions, prior preparations, if any

Prior knowledge of point, lines, angles

### Materials/ Resources needed

- Digital : Computer, geogebra application, projector.
- Non digital : Worksheet and pencil.
- Geogebra files :
**Complementary 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 right angle)
**.** - Students should be able to identify the types of angles in the file
- Let them attempt to join the two angles -They may try by coinciding different points or lines.
- Ask about the angle formed by joining the two angles?
- Challenge them to find another way to make a right angle using the two existing angles.
- Interchanging the position of the two angles – ask what they notice.
- If one angle is changed will the two together again form a complementary angle.
- Children can be asked to make note of the angle measures for different angles work sheet
- Observations made with angles seen so far.
- Ask if the angles have to be adjacent to be complementary 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 complement of angle DEF .

**Evaluation at the end of the activity**

- What are complementary pair of angles?
- Is it required for the pair of angles to be adjacent to be complementary?
- What types of angles form complementary pair?