## Key Concepts

- Classify triangles based on their sides and angles

## Types of Triangles

The triangles are classified based on sides and angles.

Based on lengths of sides, the triangles are classified as follows:

**Equilateral triangle****Isosceles triangle****Scalene triangle**

### Equilateral Triangle

A triangle in which all its three sides are equal in length is called an equilateral triangle.

**Examples:**

### Isosceles Triangle

A triangle in which two of its sides are equal is called an isosceles triangle.

**Examples:**

### Scalene Triangle

A triangle in which all three sides are unequal in length is called a scalene triangle.

**Examples:**

Based on angles, the triangles are classified as follows:

**Acute triangle****Obtuse triangle****Right triangle**

### Acute Triangle

A triangle in which all the three angles are acute (i.e., less than 90°) is called an acute-angled triangle or acute triangle.

**Examples:**

### Obtuse Triangle

A triangle in which one angle is obtuse (i.e., more than 90° but less than 180°) is called an obtuse-angled triangle or obtuse triangle.

**Examples:**

### Right Triangle

A triangle in which any one of the angles is a right angle (i.e., 90°) is called a right-angled triangle or right triangle.

**Examples:**

## Exercise

- Classify each triangle by its sides and by its angles.

### Concept map

### What have we learned

- Classfication of triangles based on sides.
- Classfication of triangles based on angles.