What is a scalene triangle?
A scalene triangle has three sides of different lengths and three angles of different sizes.
The answer
A scalene triangle has 3 sides, 3 vertices, no parallel sides and 0 lines of symmetry. The angles inside a scalene triangle add up to 180°.
Scalene triangle diagram and properties
| Property | Count |
|---|---|
| Sides | 3 |
| Vertices (corners) | 3 |
| Angles add up to | 180° |
| Right anglesA scalene triangle can have 1, like a 3, 4, 5 triangle. | 0 |
| Pairs of parallel sides | 0 |
| Lines of symmetry | 0 |
Key facts about the scalene triangle
- No two sides are equal, so no two angles are equal either.
- It has no lines of symmetry.
- A scalene triangle can be acute, right-angled or obtuse.
Where you see it
Most triangles you draw quickly by hand are scalene, and so is the shape of a ramp beside a step.
The common mistake
Thinking "scalene" means the triangle looks lopsided. It is about the measurements: a triangle is scalene only if all three sides are different.
An 11+ style question
A scalene triangle has angles of 35° and 85°. What is the third angle?
Answer: 60°
- The angles of a triangle add up to 180°.
- 35 + 85 = 120
- 180 − 120 = 60, so the third angle is 60°. All three angles are different, as they must be in a scalene triangle.
Related shapes and skills
More shapes
Questions parents ask
How many sides and vertices does a scalene triangle have?
A scalene triangle has 3 straight sides and 3 vertices (corners). Its angles add up to 180°.
How many lines of symmetry does a scalene triangle have?
A scalene triangle has 0 lines of symmetry.
Can a scalene triangle have a right angle?
Yes. A triangle with sides of 3 cm, 4 cm and 5 cm has a right angle and three different sides, so it is a right-angled scalene triangle.
Shape questions are quick marks in the 11+
Angles, symmetry, nets and 3D shapes come up in 11+ maths and non-verbal reasoning. The free diagnostic checks maths, English and both kinds of reasoning, and shows what to practise next. No card is required.