Triangles. Properties and Pythagorean Theorem
The online triangle simulations will help you to visualize graphically the characteristics and properties of triangles. We will see a visual proof of the Pythagorean theorem. We will learn what is the classification of triangles according to their sides and according to their angles and we will discover the many applications of triangles in real life.
This Thematic Unit is part of our Mathematics collection

STEM OnLine mini dictionary
Angle
The opening formed by two rays with a common origin called a vertex; its standard SI unit is the radian (rad), though it is commonly measured in degrees (°).
Cathetus
Each of the two sides that form the right angle in a right triangle.
Hypotenuse
The longest side in a right triangle, opposite the right angle.
Internal Angle
An angle formed by two adjacent sides of a polygon on its interior part.
Triangle
A polygon with three sides and three angles whose internal sum is always equal to 180°.
Triangle Height
The perpendicular segment drawn from a vertex to the opposite side or its extension.
Triangle Side
Each of the three line segments that bound the surface of the triangle.
Vertex
The joining point where two sides of a polygon meet and where the angle is formed.
What is a triangle?
Triangles are geometric figures with three sides and three angles. They are one of the most basic and fundamental shapes in Euclidean geometry. Triangles are classified according to their sides and angles.
Classification of triangles according to their sides: equilateral, isosceles and scalene triangles
In terms of sides, triangles can be equilateral, isosceles or scalene. An equilateral triangle has three equal sides, while an isosceles triangle has two equal sides and one different side. Finally, a scalene triangle has three different sides.
Classification of triangles according to their angles: acute, obtuse and right triangles
As for the angles, triangles can be acute, obtuse or right triangles. An acute triangle has all three acute angles, that is, less than 90 degrees. An obtuse triangle has one obtuse angle, that is, greater than 90 degrees. And a right triangle has a right angle of 90 degrees.
Properties of triangles
Triangles have unique properties and characteristics. The sum of the internal angles of a triangle is always equal to 180 degrees, which is one of the fundamental bases of geometry. In addition, any side of a triangle is always less than the sum of the other two sides, a property known as the triangular inequality, which ensures the viability of its shape. These properties are essential for understanding how triangles interact within more complex geometric figures, as well as in practical applications, such as the design of structures and mechanical systems where stability and precision are required.
Properties of right triangles. Pythagorean Theorem
The Pythagorean theorem is a fundamental rule in right triangles. It states that the square of the hypotenuse, which is the side opposite the 90 degree angle, equals the sum of the squares of the other two sides. Rectangular triangles are fundamental in trigonometry, where ratios such as sine, cosine and tangent are used to relate the sides and angles of these geometric figures.
Applications of triangles
In addition to their importance in Euclidean geometry, triangles are widely used in various areas, such as architecture, engineering and physics. Their simple and versatile structure makes them key elements in the construction of stable structures and in the description of natural and physical phenomena. In architecture, triangles are used to create geometric designs that distribute weight evenly and ensure the stability of buildings such as bridges and towers. In engineering, the properties of triangles are used to design mechanical and structural systems that support forces and movements. In physics, on the other hand, triangles are essential for modeling force dynamics, such as projectile trajectories and energy transmission. They also represent a fundamental component in the study of trigonometry, which is applied in fields as varied as navigation, astronomy and computational simulations.

STEM OnLine mini dictionary
Angle
The opening formed by two rays with a common origin called a vertex; its standard SI unit is the radian (rad), though it is commonly measured in degrees (°).
Cathetus
Each of the two sides that form the right angle in a right triangle.
Hypotenuse
The longest side in a right triangle, opposite the right angle.
Internal Angle
An angle formed by two adjacent sides of a polygon on its interior part.
Triangle
A polygon with three sides and three angles whose internal sum is always equal to 180°.
Triangle Height
The perpendicular segment drawn from a vertex to the opposite side or its extension.
Triangle Side
Each of the three line segments that bound the surface of the triangle.
Vertex
The joining point where two sides of a polygon meet and where the angle is formed.
Explore the exciting STEM world with our free, online, simulations and accompanying companion courses! With them you’ll be able to experience and learn hands-on. Take this opportunity to immerse yourself in virtual experiences while advancing your education – awaken your scientific curiosity and discover all that the STEM world has to offer!
Triangle simulations
Giants of science
“If I have seen further, it is by standing on the shoulders of giants”
Isaac Newton
Euclides
–
René Descartes
–
Become a giant
计算几何 | Computational Geometry
Introduction to Geometry
Computer Graphics
Polynomials, Functions and Graphs
Maths Essentials
How to Learn Math: For Students
MathTrackX: Special Functions
Professional development for Educators
Teach kids computing: Programming
Support kids’ projects: Programming with Scratch
What Works in Education: Evidence-Based Education Policies
Teach computing: Physical computing with Raspberry Pi and Python
Giants of science
“If I have seen further, it is by standing on the shoulders of giants”
Isaac Newton
Evangelista Torricelli
–
Henri Poincaré
–
Become a giant
计算几何 | Computational Geometry
Introduction to Geometry
Computer Graphics
How to Learn Math: For Students
MathTrackX: Special Functions
Pre-University Calculus
Polynomials, Functions and Graphs
Professional development for Educators
Teach computing: Introducing physical computing
HP Digital Skills for Educators – Microsoft 365 Copilot
Teach teens computing: Functions and algorithms, searching and sorting in Python
How to Learn Online
Test your knowledge
What is a triangle, and how are these geometric figures classified?
What are the fundamental properties of triangles, and why are they important?
Why are triangles so important in mathematics and real life?
What does the Pythagorean theorem state, and in which triangles does it apply?
In which fields are triangles used, and why are they so useful?
You may also be interested
Last simulations
To learn and experience
Take your knowledge to the next level with science kits and hands-on tools that connect theory with experimentation
Pythagorean Theorem

Teachers essentials
Notion
Organize your notes, tasks, and projects in one place. Notion combines notes, lists, and calendars in one flexible space.
Canva
Design presentations, diagrams, and infographics with easy-to-use templates and professional results
Genially
Create interactive content, presentations, and educational games in a simple and visual way
Desmos
The most intuitive graphing calculator to explore mathematics and create dynamic classroom activities
Tinkercad
Design in 3D and simulate electronic circuits for free; it’s the perfect tool for simple robotics projects
Your Infinite Library
Enjoy the freedom to explore millions of titles and a curated selection of magazines on any device
Join Prime for students and young adults
The best series. Millions of songs. All included with your subscription.
Science made fun
Learn with the best courses
edX
Online courses from leading universities and companies. Learn practical skills and earn professional certifications
Coursera
Courses from leading universities and companies. Learn practical skills and earn professional certifications
Udemy
Thousands of online courses tailored to your level. Learn at your own pace with expert instructors

