A vertex angle is the angle formed by two rays that meet at a common endpoint, known as the vertex. In geometry, this concept is often discussed in relation to various shapes, such as triangles and polygons. For example, in an isosceles triangle, the vertex angle is the angle opposite the base, where the two equal sides meet. In a triangle, the sum of all interior angles, including the vertex angle, is always 180 degrees. Understanding vertex angles is essential for solving problems related to triangles, polygons, and other geometric figures, as they help determine the properties and classifications of these shapes.