Basic angle facts
Sum to on lines and in triangles. around a point.
Memorise these:
| Fact | Sum |
|---|---|
| Angles in a TRIANGLE | |
| Angles on a STRAIGHT LINE | |
| Angles around a POINT | |
| Angles in a QUADRILATERAL | |
| Vertically OPPOSITE angles | equal |
Special triangles:
- Equilateral: all sides equal, all angles .
- Isosceles: two sides equal, two angles equal.
- Right-angled: one angle is .
- Scalene: all sides and angles different.
Worked qualitative. Why do angles on a line sum to ?
- A 'line' makes a half-turn ().
- All angles fitting along it must add to .
Edexcel tip. When stating an angle answer, ALWAYS give the reason: 'angles in a triangle sum to ', 'angles on a straight line sum to '.
- Triangle: .
- Straight line: .
- Point: .
- Vertically opposite: equal.
- Always state reason.