# Teaching Students About Scalene Triangles What is a Scalene Triangle? Parts and properties

A Scalene Triangle is any triangle where all three sides and angles are different lengths, just like in the illustration below. This also means that each angle has to be different. They tend to be easy to spot because they look a little wonky.

 All sides of the scalene triangle are unequal in length. There are no lines of symmetry in a scalene triangle. The angle opposite the longest side of the triangle is the most significant. E.g., a scalene triangle could have sides of 4cm, 5cm, and 8cm. It cannot be divided into two halves. See the image below for an example.

Because of their uneven qualities, scalene triangles are never symmetrical, giving them a distinctive lopsided look. Like all other triangles, the total angles in scalene triangles add up to 180°.

Types of Scalene Triangle

There are three main types of scalene triangles:

• Right-angled scalene triangle– these triangles have one angle of 90° and two more differing values. All three sides are of differing lengths.
• Acute scalene triangle– in these triangles, all three angles are less than 90°, and all three sides have differing lengths.
• Obtuse scalene triangle– these triangles have one angle over 90° and two less than 90°. Again, all three sides are of differing lengths.

Spotting a Scalene Triangle

Like all triangles, scalene triangles have three sides and three angles that all add up to 180°. The size and shape of a scalene triangle can vary a lot, but there are a few things to bear in mind that will help you to tell a scalene triangle apart from the others:

If you have a ruler available, you can measure the sides of a given triangle. If they’re all different lengths, then it is a scalene triangle.

If you have a protractor to hand, use that to measure the angles of the triangle. Again, if they’re all different, it’s a scalene triangle.

If you don’t have a way of finding out the length or angles of a triangle, it can be tricky to say for sure whether it’s a scalene or not. That said, because they’re always unsymmetrical, scalene triangles tend to have a bit of a ‘wonky’ look that can be a giveaway.