Altitude of a Triangle – Formulas, Definition With Examples

Geometry, one of the oldest branches of mathematics, plays a crucial role in our daily lives. From the structures we live in, to the screens we interact with, geometry’s influence is pervasive. At Brighterly, we believe that understanding the fundamental concepts of geometry, like the altitude of a triangle, empowers children to see the world from a different perspective. It allows them to appreciate the mathematical structures inherent in the world around them and equips them with skills to tackle more complex mathematical problems with confidence and enthusiasm.

In this article, we delve into the concept of the altitude of a triangle. We will explain what it is, its relationship with a triangle, properties it possesses, and how to derive and use formulas involving the altitude. To solidify your understanding, we have also provided examples and practice problems. This will be a comprehensive exploration that should clarify any doubts or confusions regarding the topic.

What Is an Altitude of a Triangle?

At its core, the concept of an altitude of a triangle is relatively straightforward and is a fundamental building block of geometry. Picture your regular triangle; the altitude is a line that extends from one vertex (or corner) of the triangle, down to the base (or bottom) of the triangle, forming a 90-degree, or right angle. The base can either be a side of the triangle, or an extension of a side if the triangle is obtuse.

This seemingly simple line provides a wealth of information about the triangle’s properties and its dimensions. It can help you find the triangle’s area, understand its shape better, and solve complex problems in more advanced mathematics.

Definition of a Triangle

First, let’s clarify the definition of a triangle. In simple terms, a triangle is a geometric shape that has three sides and three vertices. Each side is a straight line, and where two sides meet, it forms a vertex or point. The sum of the internal angles of any triangle is always 180 degrees.

Definition of Altitude in a Triangle

Continuing with definitions, the altitude in a triangle has a very specific meaning. The altitude is a straight line, perpendicular to the base, drawn from a vertex of the triangle to its opposite side (or in case of obtuse triangle, to its extended side). The point where the altitude meets the base (or extended base) is always at a right angle, which means it is 90 degrees.

Properties of Triangles and Their Altitudes

Properties of Triangles

As for the properties of triangles, they’re as diverse as the triangles themselves. However, there are some key attributes to remember:

  1. The sum of the angles inside any triangle is always 180 degrees.
  2. The longest side of the triangle is always opposite the largest angle.
  3. The shortest side of the triangle is always opposite the smallest angle.

These fundamental properties hold true for any type of triangle you come across, whether it’s an equilateral triangle (all sides and angles are equal), an isosceles triangle (two sides and two angles are equal), or a scalene triangle (all sides and angles are different).

Properties of Altitudes in Triangles

Now, let’s take a look at the properties of altitudes in triangles:

  1. The altitude forms a right angle with the base of the triangle.
  2. In an equilateral triangle, the altitude bisects the base and is a line of symmetry.
  3. The length of the altitude is the shortest distance from the vertex to its opposite side.

These properties are extremely helpful in problem-solving involving altitudes, particularly in finding the area of a triangle.

Difference Between a Triangle and Its Altitude

The primary difference between a triangle and its altitude is their roles in geometry. The triangle is a shape or a figure, while the altitude is a line segment associated with the triangle. The altitude is a key factor in determining many of the triangle’s properties, including its area, and the properties of other geometric figures inscribed within or circumscribed around the triangle.

Formulas Involving Altitudes of Triangles

There are several important formulas involving altitudes of triangles. The most crucial one is probably the formula to calculate the area of a triangle, given its base and altitude: Area = 1/2 * base * altitude.

Deriving the Formula for the Altitude of a Triangle

The formula for the altitude of a triangle can be derived using the Pythagorean theorem, which states that in a right-angled triangle, the square of the length of the hypotenuse (the side opposite the right angle) is equal to the sum of the squares of the lengths of the other two sides.

Writing Formulas Involving Altitude in Triangles

Consider a right triangle ABC, with BC as the base and AB as the altitude. Using the Pythagorean theorem, you can write the formula for the altitude as: AB = sqrt(AC² – BC²), where AC is the hypotenuse and BC is the base of the triangle.

Practice Problems on Altitude of a Triangle

Understanding the concept of altitude in a triangle can be further solidified by working on some practice problems. It’s an effective way to apply the theory and see the role of the altitude in practical examples.

Problem 1: Find the area of a triangle with a base of 10 units and an altitude of 5 units

The formula for the area of a triangle is 1/2 * base * altitude. If we substitute the given values, we have Area = 1/2 * 10 units * 5 units = 25 square units. So, the area of a triangle with a base of 10 units and an altitude of 5 units is 25 square units.

Problem 2: A triangle has a base of 15 units and an area of 45 square units. What is its altitude?

If we know the area of a triangle and its base, we can rearrange the area formula to find the altitude. Altitude = (2 * Area) / base. Substitute the given values, and we have Altitude = (2 * 45 square units) / 15 units = 6 units. So, the altitude of the triangle is 6 units.

These examples illustrate the importance and application of the concept of the altitude in determining key characteristics of triangles, such as their area. This concept is not only essential in mathematics but also in various fields such as engineering, architecture, and computer graphics.


In wrapping up our exploration of the altitude of a triangle, it’s important to remember that the concepts we have discussed are not just theoretical ideas, but practical tools that mathematicians, engineers, architects, and scientists use every day to solve real-world problems. The altitude is not merely a line drawn inside a triangle, it is a bridge connecting different aspects of the triangle, opening the door to a better understanding of the shape.

Brighterly believes in learning by doing, and we hope that the practice problems have helped consolidate your understanding of the concept. As you continue to explore the fascinating world of geometry, remember that every new concept you learn, like the altitude of a triangle, is a stepping stone leading you to more complex and exciting mathematical discoveries.

Frequently Asked Questions on Altitude of a Triangle

What is the altitude of a triangle?

The altitude of a triangle is a line segment that extends from a vertex (or corner) of the triangle to the base (or bottom line), forming a right angle (90 degrees) with the base. The altitude can be inside or outside the triangle depending on whether the triangle is acute or obtuse respectively.

What is the difference between a triangle and its altitude?

A triangle is a geometric shape with three sides and three vertices. The altitude, on the other hand, is a line segment associated with the triangle. It helps to determine several properties of the triangle, such as its area, and is crucial in solving complex geometric problems.

How do you calculate the altitude of a triangle?

To calculate the altitude of a triangle, you would typically need to know the area and the length of the base. The formula is: Altitude = (2 * Area) / Base. However, in a right triangle, you can also use the Pythagorean theorem if you know the lengths of the sides.

How is the altitude of a triangle used in real life?

The concept of the altitude of a triangle is used in many fields. In architecture and engineering, it helps in determining the dimensions of structures. In computer graphics, it assists in rendering realistic shapes. Even in nature, it is used to describe the flight path of a bird or the trajectory of a thrown object.

Remember, learning is a journey. Keep exploring, keep asking questions, and keep growing. The world of mathematics is vast and exciting, and the more you learn, the more fascinating it becomes. With Brighterly, you’re always one step closer to your next big discovery.

Information Sources:
  1. Triangle – Wikipedia
  2. Altitude (Triangle) – Wikipedia
  3. Geometry Practice Problems – Brighterly

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