The LessonAn equilateral triangle is a triangle that has three equal angles and three sides the same length.
Note: The lines through the sides of the triangle in the image above indicate they are of equal length. The arcs indicate the angles are equal.
Dictionary DefinitionThe Merriam-Webster dictionary defines an equilateral triangle as "a triangle in which all three sides are the same length."
Real Examples of Equilateral TrianglesBelow are real examples of equilateral triangles.
In each case
- All 3 sides are the same length.
- All 3 angles are the same (60°).
Properties of Equilateral Triangles
The Interior Angles of an Equilateral TriangleEach interior angle of an equilateral triangle is 60°.
The Symmetry of Equilateral TrianglesAn equilateral triangle has 3 lines of symmetry.
What's in a Name?'Equilateral' comes from the Latin word "aequilateralis". 'aequi' comes from the word "aequalis", meaning 'equal', and 'lateralis' means 'relating to the side'. 'Equilateral' means 'equal sides'.
The Interior Angles of an Equilateral TriangleThe interior angles of any triangle add up to 180°. Since all three angles are the same in an equilateral triangle, the 180° is divided equally between each interior angle.
This is why each angle is 60°.
Interactive Game on the Types of Triangle
- Click on a triangle so it drops into the correct "bucket."
- In total, there are 10 triangles to clear.
- If a triangle drops into the wrong "bucket," you will lose one of your three lives.
- Good luck!