Table of Contents

Last modified on April 22nd, 2021

In geometry, a triangle is a plane figure that is enclosed by three line segments.

- Side
- Angle
- Vertex

- The sum of all the angles of a triangle is equal to 180°
- The sum of the lengths of any two sides of a triangle is greater than the length of the third side
- The difference between any two sides of a triangle is less than the length of the third side
- An exterior angle of a triangle is equal to the sum of its interior opposite angles. This is called the exterior angle property of the triangle

It is the total space enclosed by the triangle. The formula is given below:

**Problem:** Finding the area of a triangle when the **BASE** and **HEIGHT** are known

**Find the area of a triangle whose base is 6 cm and height is 4 cm?**

Solution:

As we know,**A****= ½ (****b**** × ****h****)**

= ½ (6 × 4) cm

= 12 cm^{2}

**Problem:** Finding the area of a triangle when only **SIDES** are known

**Find the area of a triangle whose three sides are 3 cm, 4 cm, and 5 cm.**

Solution:

Here we will use the Heron’s formula,**A**** = √****s****(****s****–****a****)(****s****–****b****)(****s****–****c****)**, where *s* = ½ (*a*+*b*+*c*)

In this triangle, *s* = ½ (3 cm + 4 cm+ 5 cm) = 6 cm

Since, *A*= √*s*(*s*–*a*)(*s*–*b*)(*s*–*c*)

= √6(6-3)(6-4)(6-5)

= √36

= 6 cm^{2}

It is the distance covered around the edges of a triangle or simply the length of the boundary covered. The formula is given below:

**Find the perimeter of a triangle whose three sides are 4 cm, 6 cm, and 8 cm**

Solution:

As we know,**P**** = ****a ****+ ****b**** + *** c*, where a, b, c are the measure of three sides

= 4 cm + 6 cm + 8 cm

= 18 cm

Triangles are classified into two groups: **based on sides**, 1) scalene, 2) isosceles, and 3) equilateral triangles; **based on angles**, 1) acute angle, 2) obtuse angle, and 3) right or right-angled triangles.

The differences between the types are given below:

Apart from the above three types, there is **Equiangular Triangle** with all three internal angles equal to 60°and thus have all sides equal similar to an Equilateral Triangle

Last modified on April 22nd, 2021

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Thank you.

Rubaet Alam Rumon