Equilateral Triangle – Definition with Examples

At Brighterly, our mission is to make math engaging and accessible to children. By introducing them to the beauty and significance of an equilateral triangle, we foster their understanding of geometry and encourage their curiosity in exploring the world of shapes and patterns.

What is an Equilateral Triangle?

An equilateral triangle is one of the simplest, yet most fascinating concepts in geometry. It’s a triangle, a three-sided polygon, but not just any triangle. All three sides of an equilateral triangle are equal in length, hence the prefix ‘equi-‘ meaning equal. This perfect symmetry brings along a host of special properties and characteristics, making the equilateral triangle a cornerstone in the realm of geometric studies. Think of it as a perfect trio where every member is equal in contribution; that’s what an equilateral triangle stands for in the world of shapes.

Shape of Equilateral Triangle

The shape of an equilateral triangle is impeccably symmetrical. If you place it on a flat surface, you’ll notice that it balances perfectly, no matter which side is at the base. This is due to its equal sides and angles, a balance achieved only when all three sides are of the same length. It’s almost as if nature itself has used a ruler to draw each side with absolute precision, creating a shape that’s as symmetrical as it can get. You will find equilateral triangles in numerous aspects of daily life, from the logo of your favorite brand to the structure of a well-built bridge.

Properties of Equilateral Triangle

The properties of an equilateral triangle are quite intriguing. All three sides are equal, as stated before, but did you know that all three angles are also equal? Each angle measures exactly 60 degrees, summing up to the 180-degree rule for all triangles. Also, each altitude, or height, when drawn from a vertex to the midpoint of the opposite side, also bisects the vertex angle, creating two angles of 30 degrees each. The altitudes, medians, and angle bisectors coincide, making this triangle a line of symmetry. These properties make the equilateral triangle an excellent example of harmony and balance in mathematics.

Comparison: Scalene, Isosceles and Equilateral Triangles

Comparing a scalene, isosceles, and equilateral triangle, we can see that they each have unique properties. A scalene triangle has no equal sides or angles, an isosceles triangle has two equal sides and two equal angles, while an equilateral triangle outshines them both with all sides and all angles being equal. It’s like comparing different teams in a game, each having unique strategies and strengths, but the equilateral triangle is the team where all players are equally strong and coordinated.

Equilateral Triangle Formulas

Formulas play a vital role in understanding and calculating various aspects of an equilateral triangle. The area of an equilateral triangle can be calculated using the formula Area = (sqrt(3)/4) * Side^2. The perimeter of an equilateral triangle can be found by the formula Perimeter = 3 * Side. There’s also a special theorem known as the equilateral triangle theorem which states that if a triangle is equilateral, then it must also be equiangular, and vice versa.

What are NOT Equilateral Triangles?

A triangle that does not have all three sides equal is NOT an equilateral triangle. This includes isosceles triangles with only two equal sides and scalene triangles with no equal sides. Similarly, right-angled triangles, obtuse triangles, or acute triangles with unequal sides are not equilateral triangles. Remember, an equilateral triangle is the epitome of symmetry and balance, and any deviation from this symmetry does not qualify as an equilateral triangle.

Perimeter and Area of Equilateral Triangle

The perimeter and area of an equilateral triangle are quite simple to calculate, thanks to its symmetry. The perimeter is thrice the length of one side while the area is found by the formula Area = (sqrt(3)/4) * Side^2. Understanding these formulas can aid in solving various geometry problems, like finding the size of a plot or the area of a triangular park. Remember, mathematics is not just about memorizing formulas but about understanding their application in real life.

Height of Equilateral Triangle

The height of an equilateral triangle can be calculated using the formula Height = (sqrt(3)/2) * Side. It’s interesting to note that this height also bisects the base, splitting the equilateral triangle into two congruent right-angled triangles, adding yet another layer of symmetry and balance to this fascinating shape.

Centroid of Equilateral Triangle

The centroid of an equilateral triangle is the point where all the three medians of the triangle intersect. Due to the symmetrical properties of the equilateral triangle, the centroid, circumcenter (center of the circle circumscribing the triangle), and the orthocenter (point of intersection of the altitudes) all coincide at the same point. It’s like a meeting point for different aspects of the triangle, further enhancing its symmetry.


The circumcenter of an equilateral triangle is the center of the circumscribed circle that can be drawn around the triangle such that it touches all three vertices. Because of the symmetry of the equilateral triangle, the circumcenter, centroid, and orthocenter are all located at the same point, which is the center of the triangle.

Practice Problems on Equilateral Triangle

Now that we’ve covered the theory, let’s get some practice. Here are a few equilateral triangle problems to sharpen your understanding:

  1. Given that one side of an equilateral triangle is 10 units, find the area.
  2. If the perimeter of an equilateral triangle is 45 units, find the length of one side.
  3. Given that the area of an equilateral triangle is 15.588 square units, find the length of one side.


At Brighterly, we believe that learning math should be an exciting adventure, full of discovery and wonder. Throughout this exploration of equilateral triangles, we have delved deep into their definitions, properties, comparisons, and formulas. This journey has revealed the inherent beauty and significance of these special triangles, showcasing their unparalleled symmetry and their role as a fundamental building block in geometry.

Equilateral triangles have far-reaching applications in various fields, demonstrating their relevance beyond the confines of the classroom. They can be found in architectural designs, where their balanced proportions create visually pleasing structures. The height of a pyramid, for instance, can be calculated using the properties of equilateral triangles. Moreover, equilateral triangles often feature prominently in logo designs, symbolizing unity, balance, and strength. Understanding the principles behind these shapes allows us to appreciate the thought and creativity that goes into such visual representations.

Frequently Asked Questions on Equilateral Triangle

Is every equilateral triangle also an isosceles triangle?

Yes, every equilateral triangle is also an isosceles triangle. An isosceles triangle has at least two sides of equal length, and since an equilateral triangle has all three sides equal, it meets the criteria to be classified as both equilateral and isosceles.

Can an equilateral triangle be a right triangle?

No, an equilateral triangle cannot be a right triangle. In a right triangle, one of the angles measures 90 degrees, which is not possible in an equilateral triangle where all angles measure 60 degrees. If you’re interested in learning more about different types of triangles.

What is the relationship between the sides and angles of an equilateral triangle?

In an equilateral triangle, all three sides are equal in length, and all three angles are congruent, measuring 60 degrees each. The sides and angles of an equilateral triangle are interconnected and form a harmonious relationship. This unique balance is what distinguishes equilateral triangles from other types of triangles. 

How do you find the height of an equilateral triangle?

The height of an equilateral triangle can be calculated using the formula Height = (sqrt(3)/2) * Side, where “Side” represents the length of any one side of the equilateral triangle. The height is the perpendicular distance from one side to the opposite vertex. This formula allows you to determine the height of an equilateral triangle without directly measuring it. You can find more information on the properties and calculations of equilateral triangles in various geometry textbooks, such as “Geometry” by Ray C. Jurgensen and Richard G. Brown.

Information sources:
  1. Brilliant
  2. National Council of Teachers of Mathematics (NCTM)
  3. Wolfram MathWorld

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