A triangle where all three sides are different in length.

Try this Drag the orange dots on each vertex to reshape the triangle.
Try to establish a triangle that is *not* scalene. Sometimes called an irregular triangle.

Scalene triangles are triangles where each side is a different length.
They are unusual in that the are defined by what they are *not*. Most triangles drawn at random would be scalene.
The interior angles of a scalene triangle are always all different.
The converse of this is also true - If all three angles are different, then the triangle is scalene,
and all the sides are different lengths.

To see why this is so, imagine two angles are the same. The triangle would then be an Isosceles triangle, which has two sides the same length. Similarly, if all three angles are the same, it would be an equilateral triangle and all three sides would be the same length. See the entries for Isosceles and Equilateral triangles.

For more on this see Side / angle relationship in a triangle

For more on this see Side / angle relationship in a triangle

- Triangle definition
- Hypotenuse
- Triangle interior angles
- Triangle exterior angles
- Triangle exterior angle theorem
- Pythagorean Theorem
- Proof of the Pythagorean Theorem
- Pythagorean triples
- Triangle circumcircle
- Triangle incircle
- Triangle medians
- Triangle altitudes
- Midsegment of a triangle
- Triangle inequality
- Side / angle relationship

- Perimeter of a triangle
- Area of a triangle
- Heron's formula
- Area of an equilateral triangle
- Area by the "side angle side" method
- Area of a triangle with fixed perimeter

- Right triangle
- Isosceles triangle
- Scalene triangle
- Equilateral triangle
- Equiangular triangle
- Obtuse triangle
- Acute triangle
- 3-4-5 triangle
- 30-60-90 triangle
- 45-45-90 triangle

- Incenter of a triangle
- Circumcenter of a triangle
- Centroid of a triangle
- Orthocenter of a triangle
- Euler line

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