A closed structure formed by three intersecting lines is described as a triangle.

A triangle has **three sides, three angles and three vertices A, B, and C**.

A **triangle** is a polygon with all these properties.

The three angles of a triangle always **sum equal to 180°.**

**For example: **In triangles ABC, denoted as ABC. AB,BC and CA are the three sides. AB , BC , CA are three angles. **A, B, and C **are three vertices

ABC= AB + BC + CA

ABC= 60^{0} + 60 + 60

ABC= 180^{0}

## Types of Triangles

There are basically six types of triangle, which is below.

- Isosceles
- Equilateral
- Scalene
- Right Triangle
- Obtuse
- Acute

### 1.Isosceles Triangles

In this triangle only two sides are equal and two angles are equal.

### 2.Equilateral

In equilateral, all three sides are equal(AB=BC=CA) and all three angles are equal (AB = BC = CA=60^{0})

### 3. Scalene

In this type of triangle, there are no sides equal and no equal angles.

### 4.Right Triangle

In right triangle, one angle always 90°.

### 5.Obtuse Triangle

In this type of triangle One angle > 90° or more than 90°.

### 6. Acute Triangle

All angles < 90°.

## Area of Triangle

The area is 1/2 of the base times height.

“b” is the distance along the base

“h” is the height

**Area = ½ × b × h**

This formula works for all types of triangles.

### Example: What is the area of this triangle?

(Note: 100 is the height, not the length of the left-hand side)

Height = h = 100

Base = b = 40

**Area = ½ × b × h **

Area = ½ ×40 × 100 = 2000