Skip to content
Auralith Learning

Year 8 · Maths · Angles in polygons · Lesson 1

Angles in parallel lines

Use corresponding, alternate and co-interior angles in parallel lines, with straight-line and vertically opposite angle facts, giving reasons.

Whiteboard video lesson: Angles in parallel lines

28-minute video lesson

Teaching, worked examples and 20 practice questions solved step by step.

Watch free for a month

What your child will learn

  • Recall basic angle facts
  • Identify corresponding angles
  • Identify alternate angles
  • Identify co-interior angles
  • Solve multi-step angle problems with reasons

The method

  1. Corresponding angles (F shape) are equal.
  2. Alternate angles (Z shape) are equal.
  3. Co-interior angles (C shape) add up to 180°.
  4. Always give the reason, using the proper name.

Key words: parallel, corresponding, alternate, co-interior, vertically opposite.

Worked examples

The first three practice questions from the lesson, with every step.

Question 1

Angles on a straight line: 40°, 75° and x. Find x.

  1. Step 1: Angles on a straight line add up to 180°.
  2. Step 2: x = 180° − 40° − 75° = 65°

Answer: x = 65°

Question 2

Angles around a point: 120°, 95°, 80° and x. Find x.

  1. Step 1: Angles around a point add up to 360°.
  2. Step 2: x = 360° − 295° = 65°

Answer: x = 65°

Question 3

Find the size of angle x. Give a reason.

  1. Step 1: Look at the diagram
  2. Step 2: x and 65° are corresponding
  3. Step 3: Corresponding angles are equal.
  4. Step 4: x = 65°

Answer: x = 65°