Vertex – Definition with Examples

Welcome to Brighterly, where we make the world of mathematics accessible and enjoyable for children! Today, we are diving into the captivating concept of vertex angles, a foundational idea in geometry. In this comprehensive guide, we will explore the definition of vertex angles, their features, properties, and applications in various shapes. We will also discuss methods for finding vertex angles and provide engaging practice questions to help our young learners excel in this concept. Are you ready to embark on this exciting journey? Let’s get started!

What is Vertex Angle?

A vertex angle is the angle formed when two line segments or rays meet at a common endpoint, called the vertex. The vertex angle is a fundamental concept in geometry and is found in various shapes, including polygons, triangles, and even solid shapes like pyramids and prisms. By understanding vertex angles, children can better comprehend geometric shapes and their properties.

Features of a Vertex

Vertices are the points where the sides of a shape meet. For example, in a triangle, there are three vertices, while in a square, there are four. Vertices play a significant role in determining the overall properties of a shape, such as its angles, area, and perimeter. Some features of a vertex include:

  • A vertex is a common endpoint of two or more line segments or rays.
  • In polygons, the number of vertices is equal to the number of sides.
  • A vertex angle is measured in degrees, and the sum of vertex angles in a polygon depends on the number of sides it has.

Properties of a Vertex

There are several properties associated with vertices and vertex angles in geometric shapes:

  1. Polygon Angle-Sum Property: The sum of the interior angles of a polygon with ‘n’ sides is given by the formula (n-2) × 180°.
  2. Triangle Angle-Sum Property: The sum of the interior angles of a triangle is always 180°.
  3. Exterior Angle Property: The sum of an exterior angle and its adjacent interior angle in a polygon is 180°.

Vertex Angle in Solid Shapes

Vertex angles are also found in solid shapes, such as pyramids and prisms. In these three-dimensional shapes, vertices are the points where edges meet, and the vertex angle is formed by the intersection of faces.

For example, in a pyramid, the vertex angle is formed where the lateral faces meet at the apex, while in a prism, the vertex angle is formed where two lateral faces intersect along an edge.

Vertex Angle of a Parabola

In the world of conic sections, the vertex angle is crucial for understanding parabolas. The vertex of a parabola is the point at which the parabola is at its maximum or minimum value, and the vertex angle is the angle formed between the axis of symmetry and the tangent line at the vertex.

How to Find Vertex Angle?

Finding the vertex angle depends on the geometric shape you’re dealing with. For polygons, you can use the Polygon Angle-Sum Property or the Triangle Angle-Sum Property to find the sum of the interior angles, and then divide by the number of sides to get the vertex angle.

For solid shapes, like pyramids and prisms, finding the vertex angle can be more complex, as it may require knowledge of the dihedral angle between faces.

Practice Questions on Vertex Angle

  1. Find the sum of the interior angles of a hexagon.
  2. Calculate the vertex angle of a regular pentagon.
  3. Determine the vertex angle of an isosceles triangle with base angles of 40°.


At Brighterly, we believe in empowering children with a solid foundation in mathematics, and understanding vertex angles is a crucial step in achieving that goal. By learning about vertex angles, children can develop a profound appreciation for geometric shapes and their properties. This knowledge will not only enhance their problem-solving skills but will also open doors to a myriad of opportunities in their academic and professional lives. As children continue to explore the fascinating world of geometry, we are confident that they will develop the skills necessary to overcome any mathematical challenge that comes their way. Keep shining, young mathematicians!

Frequently Asked Questions on Vertex Angle

Can vertex angles be obtuse, acute, or right angles?

Yes, vertex angles can be obtuse, acute, or right angles, depending on the geometric shape. For example, in an obtuse triangle, one of the vertex angles is an obtuse angle, while in a right triangle, one of the vertex angles is a right angle.

How are vertex angles used in real-life applications?

Vertex angles are used in various real-life applications, such as architecture, engineering, and design. They help in understanding the properties and dimensions of geometric shapes, which are often used as building blocks for more complex structures.

Can vertex angles have negative values?

No, vertex angles cannot have negative values, as they are measured in degrees and represent the angle formed between two intersecting lines or rays. Angles are always positive and range between 0° and 360°.

How do you find the vertex angle in an irregular polygon?

In an irregular polygon, you can find the vertex angle by either measuring it directly using a protractor or by using given information about the shape, such as the length of sides, other angles, or the area. You might need to use trigonometry or other geometric principles to find the vertex angle in some cases.

Information Sources
  1. Wikipedia: Vertex (geometry)
  2. Wolfram MathWorld: Vertex
  3. MathPlanet: Parabolas

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