# 6+ Types of Triangles (Guide)

Welcome to our article on the different types of triangles.

Triangles are fascinating geometric shapes with a variety of characteristics.

In this article, we will explore the six main types of triangles based on their side lengths and angle measurements.

Understanding the different types of triangles can be helpful in various mathematical and practical applications.

### Key Takeaways – Types of Triangles

• There are six main types of triangles based on their side lengths and angle measurements.
• The side lengths of a triangle determine whether it is scalene, isosceles, or equilateral.
• The angle measurements of a triangle determine whether it is acute-angled, obtuse-angled, or right-angled.
• Each type of triangle has unique characteristics and properties.
• Understanding the different types of triangles is essential in various mathematical and practical applications.

## Overview – Types of Triangles

Based on Sides:

1. Equilateral Triangle:
• All three sides are of equal length.
• All three angles are equal, each measuring 60°.
2. Isosceles Triangle:
• Two sides are of equal length.
• Two angles opposite the equal sides are also equal.
3. Scalene Triangle:
• All three sides are of different lengths.
• All three angles are also different.

Based on Angles:

1. Acute Triangle:
• All three angles are less than 90°.
2. Right Triangle:
• One angle is exactly 90° (right angle).
• The side opposite the right angle is called the hypotenuse.
3. Obtuse Triangle:
• One angle is greater than 90°.
4. Equiangular Triangle:
• All three angles are equal.
• It’s essentially the same as an equilateral triangle, with each angle measuring 60°.

Each type of triangle has its unique properties and applications in various fields, including geometry, trigonometry, and real-world problem-solving.

## Triangles Based on Length of Sides

Triangles can be classified based on the length of their sides into three types.

A scalene triangle has all sides of different lengths, an isosceles triangle has two sides of equal length, and an equilateral triangle has all sides of equal length.

A scalene triangle is a triangle with all sides of different lengths. It is the most general type of triangle, as none of its sides are equal in length.

The angles of a scalene triangle also vary, with no two angles being the same. This creates a unique and versatile shape.

An isosceles triangle is a triangle with two sides of equal length. This means that the angles opposite to these equal sides are also equal to each other.

The third side of an isosceles triangle is always shorter or longer than the equal sides. Isosceles triangles have a symmetrical appearance and are often used in architectural and engineering designs.

An equilateral triangle is a triangle with all sides of equal length.

This means that all interior angles of an equilateral triangle measure 60 degrees.

Equilateral triangles are known for their symmetry and stability. They are often used in construction and design to create balance and harmony.

Triangle Type Description
Scalene Triangle A triangle with all sides of different lengths.
Isosceles Triangle A triangle with two sides of equal length.
Equilateral Triangle A triangle with all sides of equal length.

## Triangles Based on Measure of Angles

Aside from their sides, triangles can also be classified based on the measure of their angles.

The three types of triangles in this classification are the acute-angled triangle, obtuse-angled triangle, and right-angled triangle.

An acute-angled triangle is a triangle in which all angles are less than 90 degrees.

This means that all three angles of an acute-angled triangle are considered acute angles. The sum of the three angles in any triangle is always 180 degrees, so in an acute-angled triangle, all three angles must be less than 90 degrees.

On the other hand, an obtuse-angled triangle is a triangle that has one angle greater than 90 degrees.

This means that only one angle in an obtuse-angled triangle is considered an obtuse angle, while the other two angles are acute angles. The sum of the three angles in an obtuse-angled triangle is still 180 degrees, but one of the angles must be greater than 90 degrees.

A right-angled triangle is a triangle that has one angle that measures exactly 90 degrees. This angle is called the right angle, and it is formed where one of the sides of the triangle is perpendicular to another side. The side opposite the right angle is called the hypotenuse, and the other two sides are known as the legs of the triangle.

### Comparison of Triangles Based on Measure of Angles

Triangle Type Angle Measurements
Acute-angled Triangle All angles are less than 90 degrees
Obtuse-angled Triangle One angle is greater than 90 degrees, while the other two angles are less than 90 degrees
Right-angled Triangle One angle measures exactly 90 degrees, while the other two angles are acute angles

Understanding the different classifications of triangles based on the measure of their angles is useful in various mathematical and geometric applications. These classifications help identify and analyze different triangle properties, allowing for a deeper understanding of their characteristics and relationships.

## Scalene Triangle

A scalene triangle is a triangle with all sides of different lengths. It is a versatile triangle that allows for a range of possibilities in terms of angles and proportions. Unlike an isosceles or equilateral triangle, which have symmetrical properties, the scalene triangle offers a unique set of characteristics.

One distinct feature of a scalene triangle is that all of its interior angles are different from each other. This means that no two angles are equal in measure. As a result, the scalene triangle can have a combination of acute, obtuse, or even right angles within its structure.

A scalene triangle offers a sense of dynamic asymmetry, making it an interesting shape to study and explore in geometry.

When it comes to the side lengths of a scalene triangle, there are no restrictions or limitations. Each side can have a different length, which gives the triangle its unique appearance. This versatility makes the scalene triangle a valuable tool in various mathematical and architectural applications.

Properties of a Scalene Triangle
Three sides of different lengths
Three interior angles of different measures
No symmetrical properties
Allows for various combinations of acute, obtuse, and right angles

In summary, a scalene triangle is a triangle that exhibits asymmetry and versatility. Its sides and angles are all different from each other, offering a wide range of possibilities in terms of proportions and angles. This unique triangle has its own distinctive properties and is a fascinating subject for exploration in geometry.

## Isosceles Triangle

An isosceles triangle is a triangle with two sides of equal length. This means that the angles opposite to these equal sides are also equal to each other. In other words, an isosceles triangle has two congruent sides and two congruent angles.

One interesting property of an isosceles triangle is that the perpendicular bisector of the base (the side with different length) also serves as the altitude of the triangle. This means that the line segment drawn from the vertex angle (opposite the base) to the midpoint of the base is both perpendicular to the base and bisects it.

“An isosceles triangle has two congruent sides and two congruent angles.”

Moreover, the angle bisector of the vertex angle is also the median of the triangle. This means that it divides the triangle into two congruent right triangles, with the base as the hypotenuse. The length of the altitude, angle bisector, and median can be calculated using the Pythagorean Theorem and other geometric formulas.

### Properties of an Isosceles Triangle:

• Two congruent sides
• Two congruent angles
• The perpendicular bisector of the base is also the altitude
• The angle bisector of the vertex angle is also the median
Isosceles Triangle Properties
Side Lengths Two sides are equal
Angle Measure Two angles are equal
Perpendicular Bisector of Base Also the altitude of the triangle
Angle Bisector of Vertex Angle Also the median of the triangle

## Equilateral Triangle

An equilateral triangle is a special type of triangle where all three sides are of equal length. It is a symmetrical shape with three equal angles measuring 60 degrees each. The equilateral triangle is often used in various areas of mathematics, geometry, and even in art and design.

One interesting property of an equilateral triangle is that it can be used to tessellate a plane, meaning it can be repeated to completely fill a 2D space without any gaps or overlaps. This property makes it a fundamental shape in tessellation patterns and geometric constructions.

In terms of its internal angles, an equilateral triangle is made up of three acute angles, each measuring 60 degrees. This means that the sum of the interior angles of an equilateral triangle is 180 degrees, just like any other triangle.

Equilateral triangles also have interesting relationships with other geometric shapes. For example, if you connect the midpoints of the sides of an equilateral triangle, you will create a smaller equilateral triangle within, known as a medial triangle. This medial triangle also has a few unique properties worth exploring.

### Properties of an Equilateral Triangle:

• All three sides are of equal length.
• All three angles are of equal measure, each measuring 60 degrees.
• The sum of interior angles is always 180 degrees.
• It can tessellate a plane.
• Connecting the midpoints of its sides creates a medial triangle.

“The equilateral triangle is a simple yet fascinating shape that appears in various fields of study, including mathematics, geometry, and art. Its symmetrical nature and unique properties make it a fundamental figure worth exploring and understanding.”

Property Description
All Sides Equal length
All Angles Equal measure (60 degrees)
Interior Angles Sum of 180 degrees
Tessellation Can tessellate a plane
Medial Triangle Connecting midpoints creates a smaller equilateral triangle

## Acute-angled Triangle

An acute-angled triangle is a geometric shape with three angles that are all less than 90 degrees. In other words, each angle in an acute-angled triangle is small and acute. This type of triangle is unique because its angles are not only smaller than 90 degrees but also different from one another, giving it a distinct appearance.

When we examine the sides of an acute-angled triangle, we find that they can have various lengths. This means that an acute-angled triangle can be either a scalene triangle (with all sides of different lengths), an isosceles triangle (with two sides of equal length), or even an equilateral triangle (with all sides of equal length). The key defining characteristic of an acute-angled triangle lies in its angles, rather than the sides.

### Properties of an Acute-angled Triangle

Let’s take a closer look at the properties of an acute-angled triangle:

• All three angles of an acute-angled triangle are less than 90 degrees.
• Since the angles are different, the lengths of the sides can vary.
• An acute-angled triangle can have any combination of side lengths, making it versatile in its appearance.
• The sum of the lengths of any two sides of an acute-angled triangle is always greater than the length of the third side, a property known as the Triangle Inequality Theorem.

Now, let’s visualize the properties of an acute-angled triangle with a table:

Property Description
Angle Measurements All angles are less than 90 degrees.
Side Lengths The lengths of the sides can vary.
Types of Triangle Can be scalene, isosceles, or equilateral.
Triangle Inequality Theorem The sum of the lengths of any two sides is greater than the length of the third side.

## Obtuse-angled Triangle

An obtuse-angled triangle is a triangle with one interior angle greater than 90 degrees. In other words, one of the three angles in an obtuse-angled triangle is wider or more open than a right angle. This type of triangle is characterized by its unique angle measurement, which sets it apart from acute-angled and right-angled triangles.

When we look at the interior angles of an obtuse-angled triangle, we find that the sum of all three angles is still equal to 180 degrees, just like any other triangle. However, in an obtuse-angled triangle, one of the angles is greater than 90 degrees, while the other two angles are acute (less than 90 degrees).

An obtuse-angled triangle can have different combinations of angle measurements. For example, one obtuse angle can be accompanied by two acute angles, or it can have two obtuse angles with one acute angle. The specific measurements of the angles depend on the lengths of the sides and the overall shape of the triangle.

To better understand the concept of an obtuse-angled triangle, let’s take a look at the following table:

Triangle Type Angle Measurements
Obtuse-angled Triangle One angle > 90°
Acute-angled Triangle All angles
Right-angled Triangle One angle = 90°

As shown in the table, an obtuse-angled triangle stands out from the other types of triangles due to its distinguishing angle measurement. This unique characteristic makes it a fascinating subject of study in geometry and offers a diverse set of possibilities for mathematical exploration.

## Right-angled Triangle

A right-angled triangle is a special type of triangle that has one interior angle measuring exactly 90 degrees. This makes it unique among the various types of triangles.

The side opposite the right angle is called the hypotenuse, and it is the longest side in the triangle. The other two sides are known as the legs of the triangle. The relationship between the lengths of the sides in a right-angled triangle is governed by the Pythagorean theorem, which states that the square of the hypotenuse is equal to the sum of the squares of the legs.

Right-angled triangles have numerous applications in various fields, including mathematics, physics, and engineering. They are often used to solve problems involving distances, heights, angles, and more. The 90-degree angle in a right-angled triangle allows for easy calculation and simplification of complex problems.

## FAQ – Types of Triangles

### What are the different types of triangles based on the length of their sides?

There are three types of triangles based on the length of their sides: scalene triangle, isosceles triangle, and equilateral triangle.

### How are scalene triangles defined?

Scalene triangles have all sides of different lengths and all interior angles that are different from each other.

### What defines an isosceles triangle?

Isosceles triangles have two sides of equal length, and the angles opposite these equal sides are also equal to each other.

### What is an equilateral triangle?

An equilateral triangle has all sides of equal length, and all interior angles of an equilateral triangle measure 60 degrees.

### What are the different types of triangles based on the measure of their angles?

Triangles can be classified based on the measure of their angles as acute-angled triangles, obtuse-angled triangles, and right-angled triangles.

### How are acute-angled triangles defined?

Acute-angled triangles have all angles less than 90 degrees.

### What is an obtuse-angled triangle?

An obtuse-angled triangle has one interior angle greater than 90 degrees.

### What defines a right-angled triangle?

A right-angled triangle has one interior angle equal to 90 degrees. The side opposite the right angle is called the hypotenuse.