**Definition of Diagonal Line**

- The line joining any two non-adjacent vertices of a polygon is called diagonal line.

**More about Diagonal Line**

- The number of diagonals of a polygon can be calculated using the formula

d =, where*S*is the number of sides in the polygon.

The number of diagonals in a polygon with 5 sides = = 5.

**Example of Diagonal Line**

- In the given figure, A and C, B and D are the non-adjacent vertices.

The line joining any of these pairs of vertices is called diagonal of the figure.

So, AC and BD are the diagonals of the given figure.

**Solved Example on Diagonal Line**

Find the number of diagonals in a regular hexagon.

Choices:

A. 9

B. 6

C. 12

D. 3

Correct Answer: A

Solution:

Step 1:A regular hexagon has all of its sides and angles congruent.

Step 2:Draw the diagonals in a regular hexagon.

Step 3:9 diagonals are formed joining the non-adjacent vertices.

Step 4:So, there are 9 diagonals in a regular hexagon.

**Related Terms for Diagonal Line**

- Adjacent
- Polygon
- Vertices