Triangle  Definition with Examples
What is a Triangle?
Triangle Definition: A triangle is a closed 2dimensional shape formed by joining 3 line segments.
Triangles Around Us
Triangles are found in food items, in structures of the buildings, in signboards etc.
Parts of a 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 TriangleAll sides are equal. All angles are equal and measure 60°. 
Isosceles Triangle2 sides are equal. Angles opposite to equal sides are equal. 
Scalene TriangleNo side or angle are equal. 
On the Basis of Angles 
Acute TriangleAll angles measure < 90°

Right TriangleOne angle measure = 90°

Obtuse TriangleOne angle measure > 90° 
The triangles can be categorized on the basis of their angles and sides as follows:
Right Isosceles TriangleOne angle measure = 90° Two sides are equal. 
Obtuse Scalene TriangleAll angles measure < 90° All sides are equal. 
Triangles are introduced at math elementary level under the domain geometry.
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