Common Core Math Vocabulary

Triangle - Definition with Examples

What is a Triangle?

Triangle Definition: A triangle is a closed 2-dimensional shape formed by joining 3 line segments.

Triangles Around Us

Triangles are found in food items, in structures of the buildings, in signboards etc.

Triangle Around us

 

Parts of a Triangle

Properties of Triangle

  • The line segments joined to form a triangle are known as the sides of the triangle.
  • The points where the sides of a triangle meet are known as the corner/vertex of the triangle. More than one vertex are called vertices.
  • The angle formed at each of the vertices of the triangle are known angles of triangles.

 

A triangle has 3 angles, 3 sides, and 3 vertices.

Sum of all angles of a triangle is 180 degree.

 

Classification of Triangles

A triangle is classified by its sides and by its angles.

On the Basis of Sides

Equilateral Triangle

Equilateral Triangle

All sides are equal.

All angles are equal and measure 60°.

Isosceles Triangle

Isosceles Triangle

2 sides are equal.

Angles opposite to equal sides are equal.

Scalene Triangle

Scalene Triangle

No side or angle are equal.

On the Basis of Angles

Acute Triangle

Acute Triangle

All angles measure < 90°

 

Right Triangle

Right Triangle

One angle measure = 90°

 

Obtuse Triangle

Obtuse Triangle

One angle measure > 90°

The triangles can be categorized on the basis of their angles and sides as follows:

Right Isosceles Triangle

Right Isosceles Triangle

One angle measure = 90°

Two sides are equal.

Obtuse Scalene Triangle

Obtuse Scalene Triangle

All angles measure < 90°

All sides are equal.

Triangles are introduced at math elementary level under the domain geometry.

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