Triangles
A triangle is a closed shape with 3 angles, 3 sides, and 3 vertices. A triangle with three vertices says P, Q, and R is represented as △PQR. It is also termed a threesided polygon or trigon. In this minilesson, we will explore everything about triangles, which are commonly seen around us. If you observe the shape of signboards and your favorite sandwiches it forms the shape of a triangle.
1.  Parts of Triangle 
2.  Classification of Triangles 
3.  Formulas of a Triangle 
4.  Solved Examples on Triangles 
5.  Practice Questions on Triangles 
6.  FAQs on Triangles 
Parts of Triangle
A triangle consists of various parts. It has 3 angles, 3 sides, 3 vertices. Let us learn the concept with the help of a triangle figure given below. Look at the triangle PQR.
In the above image:
 The three angles are, ∠PQR, ∠QRP, and ∠RPQ.
 The three sides are side PQ, side QR, and side RP.
 The three vertices are P, Q, and R
Classification of Triangles
According to two major elements, triangles can be classified as :
 On the basis of angles
 On the basis of the measurement of their sides.
Let us understand the classification of triangles with the help of the table given below. The table gives information about the difference between 6 different types of triangles on the basis of angles and sides.
Note: The sum of all the angles of the triangle is equal to 180°.
Formulas of a Triangle
In geometry, for every twodimensional shape, there are always two basic measurements we need to find out, i.e., the area and perimeter of that shape. Similarly, the triangle has two basic formulas which help us to determine its area and perimeter. Let us discuss the formulas in detail.
Perimeter of Triangle
The perimeter of a triangle is the sum of all three sides of the triangle. Consider △ABC.
In the above figure, the three sides of the triangle are represented as AB= c, AC = b, and CB = a respectively.
The perimeter of a triangle is the sum of all three sides AB + BC + CA.
Perimeter of Triangle formula = a + b + c units
Half of the perimeter of the triangle is termed as Semi Perimeter of Triangle. It is given as (a + b + c)/2 units.
Area of a Triangle
The area of a triangle is the space covered by the triangle. It is half the product of its base and altitude (height). It is always measured in square units, as it is twodimensional. Look at the given triangle ABC.
Area of ΔABC = 1/2 × AD × BC square units.
Here, BC is the base and AD is the height of the triangle.
Important Notes
 A triangle cannot have a measurement or value of all the angles less than 60°.
 A triangle is a 3sided closed shape.
 There are two important formulas related to triangles, i.e., Herons formula and Pythagoras theorem.
 The sum of the angles of a triangle adds up to 180° and given as ∠1 + ∠2 + ∠3 = 180°.
Related Articles on Triangles
Check out these interesting articles to know more about triangles and topics related to triangles.
 Properties of Triangle
 Scalene Triangle
 Equilateral Triangle
 Right Angled Triangle
 Triangle Calculator
 Scalene Triangle Formula
 Right Triangle Calculator
 Isosceles Triangle Perimeter Formula
 Area of Isosceles Triangle
 Area of Equilateral Triangle
 Area of Right Triangle
 Area of Scalene Triangle
 Acute Triangle
Solved Examples on Triangles

Example 1: The perimeter of a triangular garden is given as 26 feet. If two of its sides measure 7 feet and 11 feet respectively, what is the measure of the third side?
Solution:
We know that the perimeter of a triangle is the sum of all three sides.
⇒ 26 = 7 + 11 + unknown side
Therefore, the unknown side is given by:
=26−(7+11) = 8 feet
∴ The third side of the given triangle measures 8 feet. 
Example 2: Emma is building a triangular wooden birdhouse. If two of the angles measure 45° and 63°, what is the measure of the third angle?
Solution:
We know that the sum of the angles of a triangle adds up to 180°. Therefore, the unknown angle is:
= 180° − (45° + 63°) = 72°
∴ The measurement of the third angle is 72°. 
Example 3: The height of the triangular park is 360 feet and the side is 270 feet. Find the area of the park.
Solution:
The height of the triangle = 360 feet and base = 270 feet
The area of a triangle is = 1/2 × Base × Height
Area of the triangular park = 1/2 × 270 × 360 = 48600 feet^{2}
∴ Area of the triangular park = 48,600 feet^{2}
FAQs on Triangles
Are Isosceles Triangles Always Acute?
No, an isosceles triangle can be an acute angle, right angle, or obtuseangled triangle depending upon the measure of the angles it has.
What is the Area of Scalene Triangle?
The area of the scalene triangle is used to find the area occupied by the scalene triangle within its sides. The area of the scalene triangle is half of the product of the base to the height of the scalene triangle. Thus, the area of the scalene triangle, with a base "b" and height "h" is given as "1/2 × b × h".
What is the Formula Used for Finding the Area of a Right Triangle?
The formula used for finding the area of a right triangle of base (b) and height (h) is 1/2 × base × height (or) 1/2 × b × h.
What is an Equilateral Triangle?
An equilateral triangle is a regular polygon (trigon) with three equal sides. Equilateral triangles also have three equal angles which measure 60 degrees each and sum up to 180 degrees.
What is an Isosceles Triangle?
In a triangle, if the length of only two sides is equal and the measure of corresponding opposite angles is also equal, then the triangle is said to be an isosceles triangle.
What is a Right Triangle in Geometry?
A right triangle is a triangle with one angle measurement as 90 degrees (right angle). In geometry we have three different names for all the three sides of a right triangle which are listed below:
 The hypotenuse (longest side or the side opposite to 90° angle.)
 The base
 The perpendicular (altitude).