A closed plane geometric figure, which formed by the three line segments is called triangle.

The word, triangle is formed by a prefix “tri” and a word “angle“. The meaning of tri is three. According to these two meanings, triangle is three angles.

Geometrically, three line segments can only form three angles when their endpoints are connected each other as a closed geometric figure. Hence, the closed plane figure, formed by the three line segments which can only form three angles is known as triangle geometrically.

For studying the triangles, we have to learn the following three fundamental concepts.

A point where two line segments get intersected in a triangle is called a vertex of a triangle.

A straight line segment that joins any two vertices of a triangle is called a side of a triangle.

An angle between two sides of a triangle at their respective vertex is called an angle of a triangle.

Learn how to construct a triangle in geometry

List of different types of triangles with their geometrical construction and examples.

List of properties of triangles with understandable proofs.

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