Parallel lines

In addition to the basic angle facts, you need to memorise the rules of angles and parallel lines, and apply these to problems.

Small arrows are used to show that 2 lines are parallel to each other.

Click on the button below to see examples of these different types of angle.

• Vertically opposite angles are equal.
• Corresponding angles are equal.
• Alternate angles are equal.
• Co-interior angles add up to 180°.

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When answering questions on angles, remember the following points:

• Look out for parallel lines (squares, rectangles, parallelograms and marked parallel lines) and see which of the above rules apply.
• Look out for lines of equal length. Remember that an isosceles triangle has two sides of equal length and that the angles which are directly opposite these sides are also equal.
• Diagrams are unlikely to be drawn to scale, so do not be tempted to measure!
• Do not assume things which may turn out to be untrue (for example, an angle is not necessarily a right angle just because it looks as though it should be!).
• It is likely that you will not be able to find the required angle immediately. Do not worry - just write as much information as possible onto the diagram. It should eventually lead you to the answer. If not, you might still get some marks for your working!

Now try a Test Bite