What Is a Triangle?

A figure with three sides (or edges) and three corners (or vertices) is called a triangle. Below you see five different triangles.

As you can see, a triangle’s sides may have different lengths, so that some triangles are big, and others are small. Some triangles slant distinctly, while others are pretty straight. Some triangles are tall and narrow, while others are short and stout.

Even though these triangles look different, they all have three sides and three corners. Check if all the triangles above have three sides and three corners. If you count, and find that one of them has anything different than three sides and corners, count again! They are all triangles.

Types of Triangles

Some triangles have special properties, for which they have been given special names. Let’s take a look at them.

Equilateral Triangles

A triangle is said to be equilateral if all the sides of the triangle have the same length. All the angles in an equilateral triangle have the same size.

Isosceles Triangles

A triangle is said to be isosceles if two of the sides of the triangle have the same length. Two of the angles in an isosceles triangle have the same size.

Right Triangles

A triangle is said to be a right triangle if one of its angles is a right angle ($90$${}^{\circ }$).

Scalene Triangles

A scalene triangle is a triangle where all the sides have different lengths, and none of the angles are right angles.