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Basic geometry terms for OCR GCSE Maths

Basic geometry terms

This page covers the following topics:

1. Angles at a point
2. Angles at a point on a straight line
3. Vertically opposite angles
4. Alternate angles
5. Corresponding angles

The sum of the angles at a point is 360ยบ. This property can be used to find the value of missing angles.

Angles at a point

The sum of the angles at a point on a straight line is 180ยบ. This property can be used to find the value of missing angles.

Angles at a point on a straight line

Vertically opposite angles are angles which are opposite each other at a point. These angles are equal.

Vertically opposite angles

Given two parallel lines, the marked angles on the line joining the two parallel lines are equal. These angles are called alternate angles or Z angles.

Alternate angles

The angles between two parallel lines and a third intersecting lines, as shown on the diagram, are equal. These angles are called corresponding angles or F angles.

Corresponding angles

1

State all the pairs of vertically opposite angles on the given diagram.

The pairs of vertically opposite angles are a and d, b and e, and c and f.

State all the pairs of vertically opposite angles on the given diagram.

2

Calculate the value of y.

The 98ยบ angle and y are corresponding angles, therefore they are equal and y = 98ยบ.

Calculate the value of y.

3

Calculate the value of angle a.

a = 360 โˆ’ (15 + 95 + 10 + 15) = 225ยบ.

Calculate the value of angle a.

4

Find the value of b, given that d = 78ยบ and f = 83ยบ.

Using the sum of angles on a straight line, e = 180 โˆ’ (78 + 83) = 19ยบ.
Angle b is the vertically opposite angle to e, therefore b = e = 19ยบ.

Find the value of b, given that d = 78ยบ and f = 83ยบ.

5

Use alternate angles to find the value of ฮธ.

The angle next to the 112ยบ angle is 180 โˆ’ 112 = 68ยบ.
This is an alternate angle to ฮธ, therefore the two are equal and a = 68ยบ.

Use alternate angles to find the value of ฮธ.

End of page

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