Triangle (An Introduction), Types & Area of triangle

What is a triangle?

A Polygon which has three sides or three edges and three vertices is known as the triangle. The sum of all 3 angles of a triangle always equals to 180°. Three or two sides of the triangle can be equal and unequal in the triangle and it depends on the type of triangle.

Type of triangle on the basis of sides

There are seven types of the triangle and their names are mentioned below:

1. Equilateral triangle: one whose three equal sides and equal angles. All angle is 60°.

2. Isosceles triangle: one whose two sides are equal and equal angles.

3. Scalene triangle: one whose all sides are not equal.



Equilateral triangle

Three Side equal

Isosceles triangle

Two Side equal

Scalene triangle

No Side equal

Type of triangle on the basis of sides

1. Right triangle: one whose one angle is right angle(90°).

2. Acute triangle: one whose all angle is acute angle.

3. Obtuse triangle: one whose one angle is obtuse angle.

4. Oblique triangle: An oblique triangle is any triangle that is NOT a right triangle. Acute triangles and obtuse triangles are oblique triangles.



Acute triangle

all angle is acute

Obtuse triangle

one angle is obtuse

Right triangle

one angle is right angle (90°)

Area of a triangle

In case of calculating the area of a triangle, you have to multiply the base of the triangle by the height of the triangle and then divide by 2. So, the digit you will get, it will be the area of that triangle.

Formula to find the area of a triangle: –

Area = base x height2

b is base of the triangle & h is the height of triangle.

Find the area of the triangle which has base 10 cm and height 9 cm?

b = 10 cm
h = 9 cm
Formula to find the area of triangle is,
A = (b x h)2
A = (10 x 9)2
A = 902
A = 45 cm2

Find the area of triangle without the height

When, in any question the height has not given, then we use the Hero’s formula.
Hero’s formula for finding the area of a triangle is:

√s (s-a) (s-b) (s-c)

In this formula,
S is stand for the semi-perimeter or half perimeter and a, b, c are the sides of triangle

Example: Find the area of triangle a = 9, b = 7, c= 4 and s = 10

What is the perimeter?

The perimeter is the length of the boundary of any polygon. In other words, the perimeter can be also defined as the path surrounded by any polygon. The word perimeter derives from the Greek word “peri” which means around and “metron” means measure. The total length of the side of any polygon is referred to as perimeter.

Formula to find the perimeter of a triangle:

The perimeter of triangle ABC


AB, BC, and CA are referring the three sides of a triangle.

Find the perimeter of the triangle which has AB = 8 cm, BC = 13 cm and CA= 11 cm.

The formula for finding the perimeter of triangle ABC= AB + BC + CA

AB = 8 cm
BC = 13 cm
CA = 11 cm

After applying the value in formula,

Perimeter of triangle ABC = 8 + 11 + 13
= 32 cm

I hope this, the article will help you to prepare for an RRB NTPC exam. If you have any question related to the article, you can post it into the comment section. You will get a reply shortly.

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