# Stage 4 – angles

## Strategy

Students can:

• identify acute, obtuse, reflex, right, straight, revolution, vertically opposite, complementary, supplementary, alternate, corresponding and co-interior angles
• calculate the size of these angles

## Activities to support the strategy

### Activity 1

1. Students revise the basic angle types of acute, obtuse, reflex, right, straight, revolution by matching angle type and diagram in the worksheet Basic angles. View/print (PDF 217.8KB)

2. Teacher introduces angle types and properties of adjacent angles, vertically opposite angles, complementary angles and supplementary angles. Students calculate the size of each angle in the worksheet Size of angle (PDF 199.28KB). View/print (PDF 199.28KB)

3. Students practise calculating the size of angles and listing appropriate reason, using:

### Activity 2

1. Students use Mathsisfun/geometry/parallel-lines to identify angles formed by 2 parallel lines and a transversal.

2. Students use activities to determine that:

• alternate angles are equal when lines are parallel

Also refer to mathopenref.com/anglesalternateinterior

• corresponding angles are equal when lines are parallel

Also refer to mathopenref.com/anglescorresponding

• co-interior angles are supplementary when lines are parallel

Also refer to mathopenref.com/transversal for a demonstration of angles remaining equal when lines are parallel.

3. Name the angle types formed by 2 parallel lines and a transversal. View/print

4. Determine size of angles and list reasons. View/print

## References

### Australian curriculum

ACMMG163: Identify corresponding, alternate and co-interior angles when two straight lines are crossed by a transversal. ACMMG164: Investigate conditions for two lines to be parallel and solve simple numerical problems using reasoning

### NSW syllabus

MA4-17MG: Classifies, describes and uses the properties of triangles and quadrilaterals, and determines congruent triangles to find unknown side lengths and angles.