RulesMath · P4 to P6Angles
Angles Must-Know Rules
The 6 rules that unlock every angle question.
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Angle rules
Angles on a straight line make 180°.
1
Straight Line
Angles on a straight line add up to 180°.
2
Point
Angles around a point add up to 360°.
3
Triangle
Interior angles of a triangle add up to 180°.
4
Quadrilateral
Interior angles of a 4-sided shape add up to 360°.
5
Vertically Opposite
When two lines cross, opposite angles are equal.
6
Isosceles Triangle
The two base angles are equal.
Common Mistakes
- Assuming a triangle is isosceles without proof
- Confusing 180° and 360° rules
- Skipping the reason line in working
Teaching Team Tip
Always write the reason (e.g. 'angles on a straight line') next to your working.
Worked Example
Try it, then check the steps
Question
In triangle ABC, ∠A = 50°, ∠B = 60°. Find ∠C.
Steps
- 1Sum of angles in triangle = 180°
- 2∠C = 180° − 50° − 60°
- 3∠C = 70°
What to do next
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