Triangles are fundamental shapes in geometry with three straight sides and three angles. They come in many different types, each with unique properties.
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= 600 + 60 + 60
ABC= 1800
Types of Triangles
There are basically six types of triangle, which is below.
- Isosceles Triangle
- Equilateral Triangle
- Scalene Triangle
- Right-angled Triangle
- Obtuse Triangle
- Acute-angled Triangle
1.Isosceles Triangles
In this triangle only two sides are equal and two angles are equal.
2.Equilateral Triangle
In equilateral, all three sides are equal(AB=BC=CA) and all three angles are equal (AB = BC = CA=600)
3. Scalene Triangle
In this type of triangle, there are no sides equal and no equal angles.
4.Right Triangle
In the 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 of Triangle = ½ × b × h
This formula works for all types of triangles.
Example: What is the area of a 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