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# Difference Between Diameter Diagonal

A circle is a geometric shape in which the locus of a point on a plane such that the distance of that point is constant from a fixed point on that same plane; this fixed point is called the centre of the circle, and the constant distance from the centre is called the radius of the circle. Similarly, a sphere is a three-dimensional closed figure whose surface is a set of points in a space equidistant to a fixed point, called the centre of the sphere. A polygon is a closed two-dimensional curve made of line segments. These line segments are called edges or sides of a polygon, and the common point of two edges is called vertices. For example, triangle, quadrilateral, pentagon etc. A polyhedron is a three-dimensional closed figure whose faces are a polygon. Some examples of polyhedrons are cube, cuboid, prism etc. Let us briefly discuss diameter and diagonal as a part of a circle, sphere, polygons and polyhedrons and differentiate between them.

## Diameter of a Circle

The chord of a circle is a line segment within the circle that joins any two points on the circle. And hence the longest chord of a circle that passes through the centre of the circle is called the diameter of the circle.

 Diameter is the most extended chord within a circle that passes through the centre of the circle.It is twice the radius of the circle, or half of the diameter is equal to the radius of the circle.It divides a circle into two equal parts.It is a line segment within a circle whose midpoint is the circle’s centre.

Now that we have seen what diameter is let us briefly discuss what is diagonal before making a differentiation between them.

## What is Diagonal?

For any closed curve made of line segments, whether 2-dimensional or 3-dimensional, a diagonal of a shape is a line segment that joins two vertices of the shape other than the edge of the shape.

Hence, a diagonal is a line segment whose endpoints are two non-adjacent vertices of the figure.

 Diagonal is a part of polygon or polyhedron and is a line segment that joins two non-adjacent vertices of the shape.The number of diagonals of a polygon with n vertices is given by the formula [n(n−3)]/2.Triangle is the only polygon that does not have a diagonal.Three-dimensional shapes have two types of diagonals – Body/Space Diagonals and Face Diagonals.

## Difference Between Diameter and Diagonal

 Diameter Diagonal It is a line segment within a circle joining any two points on the circle and passing through its centre.It is part of a circle, sphere or hemisphere.There can be an infinite number of diameters drawn within a circle.It may be a slanted or straight-line segment.It divides a circle or a sphere into two equal parts.For any circle, the diameter is twice the radius of the circle. It necessarily lies in the interior of the circle or sphere. It is a line segment that joins any non-adjacent vertices of a polygon or a polyhedron.It is a part of a polygon or a polyhedron.A polygon or a polyhedron has a finite number of diagonals.It is a necessarily slanted or oblique line segment.A diagonal does not always divide the shape into equal parts.The diagonal length depends on the length of the edges of a given regular polygon or polyhedron.It may lie on the exterior of the shape. For example, in the case of a concave polygon, its diameter lies in the exterior.

Hence, diameter is related to a circle, and all its geometrical properties are related to the properties of a circle. In contrast, a diagonal is associated with a polygon. Despite both being a line segment joining any two points on a geometric figure, they are different.

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