Pythagoras Theorem – Formula, Definition With Examples

Welcome, math enthusiasts! Here at Brighterly, we are dedicated to making math engaging and accessible for kids around the globe. In today’s journey into the magnificent world of mathematics, we’ll be exploring the remarkable Pythagoras Theorem, a cornerstone of geometry that has held its ground for over two millennia!

This theorem, named after the ancient Greek philosopher and mathematician Pythagoras, provides us a deep understanding of the relationship between the sides of a right-angled triangle. Its broad applications, ranging from calculating distances to constructing intricate structures, make it an essential pillar of not only geometry but also fields like physics, engineering, and computer science.

Introduction to Pythagoras Theorem

Let us take an exciting journey today into the world of geometry, exploring the foundations of one of its most important principles, the Pythagoras Theorem. Geometry, the branch of mathematics that is concerned with the properties and relations of points, lines, surfaces, solids, and higher dimensional analogs, presents us with the fascinating theorem that helps us solve complex problems and equations.

The Pythagoras theorem, named after the ancient Greek mathematician Pythagoras, is one of the most widely recognized and utilized mathematical concepts. Its broad range of application, from calculating distances to building complex structures, makes it a cornerstone of geometry and trigonometry. For our younger readers at Brighterly, this theorem serves as an essential building block in your journey to understanding and mastering math.

Who Was Pythagoras?

Before we delve into the theorem, it’s only fair to understand who Pythagoras was. He was an ancient Greek philosopher and mathematician who lived around 570–495 BC. Pythagoras is known for many intellectual achievements, but his most enduring legacy remains in the field of mathematics.

As the founder of the influential Pythagoreanism movement, Pythagoras and his followers were known to view numbers as a universal language. They believed numbers had a divine and mystical significance. His biography illustrates how his philosophies and mathematical principles continue to influence modern mathematical thought.

Definition of the Pythagorean Theorem

The Pythagorean Theorem states that in a right-angled triangle, the square of the hypotenuse’s length (the side opposite the right angle) is equal to the sum of the squares of the lengths of the other two sides. This can be written as: a² + b² = c², where c represents the length of the hypotenuse, and a and b represent the lengths of the other two sides.

This definition provides a fundamental principle for determining the length of any one side of a right-angled triangle as long as the lengths of the other two sides are known.

Formula of the Pythagorean Theorem

The formula of the Pythagorean theorem, a² + b² = c², is derived from the definition. This simple equation is a powerful tool, helping us solve a wide array of mathematical and real-life problems.

In this equation, a and b are the lengths of the two legs of the triangle (the sides that form the right angle), and c is the length of the hypotenuse. This formula applies to any right-angled triangle, regardless of its size or proportions.

Explanation of the Pythagorean Theorem

To better understand the Pythagorean theorem, let’s visualize it. Imagine you have a right-angled triangle. You draw a square on each side of the triangle. The area of the square drawn on the hypotenuse (c²) will be equal to the sum of the areas of the squares drawn on the other two sides (a² and b²). Thus, a² + b² = c².

This principle applies universally to all right-angled triangles, and it allows us to calculate unknown side lengths when we know the other two sides. This theorem creates a powerful and universal relationship between the lengths of the sides of a right triangle.

Properties of the Pythagorean Theorem

The Pythagorean theorem has several important properties. One key property isits reversibility. That means, if the square of one side length equals the sum of the squares of the other two side lengths, then the triangle must be a right-angled triangle.

Another interesting property of this theorem is its ability to help us classify triangles. If c² > a² + b², the triangle is obtuse-angled, and if c² < a² + b², the triangle is acute-angled. Remember, c represents the longest side in these cases.

The Proof of the Pythagorean Theorem

The proof of the Pythagorean theorem has been demonstrated in numerous ways throughout history. One of the most famous proofs is the one given by Euclid in his work, “Elements”.

In this proof, Euclid constructs a square with each side being a + b (the lengths of the two legs of the triangle), and he shows that this large square’s area can be computed in two different ways. Once by summing the area of one square of side length c (the hypotenuse) and two rectangles of sides a and b. And again, by summing the areas of two squares of sides a and b.

Both methods yield the same total area, proving the theorem. You can find a more detailed explanation of Euclid’s proof here.

Applications of the Pythagorean Theorem

The Pythagorean theorem finds application in numerous mathematical and scientific fields. It’s essential for solving problems in algebra, geometry, trigonometry, physics, computer science, and even in the realms of art and architecture.

In computer graphics, for instance, it’s used to calculate pixel distances. In physics, it’s used to determine the shortest path or the ‘resultant’ of two vectors. The theorem is a fundamental element of the calculations involved in GPS navigation, game development, construction, and many other industries.

Real World Examples of the Pythagorean Theorem

Several real-world examples highlight the practical use of the Pythagorean theorem. For instance, architects and builders often use the theorem to ensure that walls or structures are perpendicular.

In sports, the theorem helps calculate the shortest distance a player has to cover. For example, in baseball, a player running from first base to third can run diagonally, which is the hypotenuse of a right triangle, instead of running to second base then to third, effectively saving time and energy.

Problems Solved Using the Pythagorean Theorem

One classic problem solved using the Pythagorean theorem is finding the shortest distance between two points in a plane. If you have two points in a Cartesian plane, you can treat these points as the vertices of a right-angled triangle (with the third vertex being where the perpendicular from one point meets the horizontal line through the other point). The theorem can then be used to calculate the hypotenuse, giving the shortest distance between the points.

Writing Equations using the Pythagorean Theorem

Writing equations using the Pythagorean theorem requires understanding the relationship between the sides of a right triangle. Let’s consider a right triangle with side lengths a, b, and c. If you know the lengths of two sides and want to find the third, you can rearrange the theorem’s formula, a² + b² = c², to solve for the unknown side.

For example, if you know a and b and want to find c, you just plug the known values into the formula and solve for c. If you know c andone of the other sides, you can rearrange the formula to solve for the unknown side. For example, if you know c and a, you can rearrange the formula to b² = c² – a² to find b.

Practice Problems on the Pythagorean Theorem

Practicing problems on the Pythagorean theorem is an excellent way to get a better understanding of the concept. Here are a few examples to get started:

  1. Given a right triangle with legs 6 cm and 8 cm long, how long is the hypotenuse?
  2. A ladder 10 m long leans against a wall. The foot of the ladder is 6 m away from the wall. How high is the ladder’s top from the ground?
  3. If the hypotenuse of a right-angled triangle is 13 cm and one of its legs is 5 cm, what is the length of the other leg?


We hope this exploration of the Pythagoras Theorem has brought you closer to understanding one of the fundamental concepts in geometry. We’ve traveled from the ancient lands of Greece to modern-day applications, uncovering the true essence and magic of Pythagoras’ theorem. At Brighterly, our mission is to make learning fun and easy. We believe that understanding such pivotal concepts can ignite a lifelong love of learning and empower you to solve the complex problems of tomorrow.

As we conclude our journey today, remember, mathematics is not just about numbers, equations, or algorithms. It’s about understanding! With every problem you solve, you’re not just learning math, you’re exploring a universal language that transcends cultural and linguistic boundaries. So keep exploring, stay curious, and most importantly, have fun with math!

Frequently Asked Questions on Pythagoras Theorem

Is the Pythagorean theorem only for right triangles?

Yes, indeed! The Pythagorean theorem is specifically designed for right-angled triangles, where one angle measures exactly 90 degrees. The theorem beautifully encapsulates the relationship between the sides of a right triangle, allowing us to calculate the length of one side given the lengths of the other two sides.

Can the Pythagorean theorem be used in three dimensions?

Absolutely! While we typically learn the Pythagorean theorem in the context of two-dimensional geometry, it can indeed extend into three dimensions. This expanded version is known as the 3D Pythagorean theorem, where the length of a line in 3D space can be found using the formula: d² = a² + b² + c², where d is the length of the line and a, b, and c are the distances in the x, y, and z directions, respectively.

Can the Pythagorean theorem be wrong?

The Pythagorean theorem is a well-established mathematical principle that holds true for all right-angled triangles. However, it’s important to apply it correctly. Misapplications, such as trying to use it on a non-right triangle, can lead to inaccurate results. But as long as you’re working with a right-angled triangle, the Pythagorean theorem will never let you down! It’s a constant, reliable tool in our mathematical toolkit.

Information Sources
  1. Euclid’s Elements & The Pythagorean Theorem – Clark University
  2. History of the Pythagorean Theorem – Saint Louis University
  3. The Pythagorean theorem – University of California, Davis

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