Which undefined term is needed to define an angle?

plane
point
ray
line

Point.

Further explanationThe angle is determined by three points, we call it A, B, C, with A ≠ C and B ≠ C.  We express an angle with three points and a symbol ∠. The middle point represents constantly vertex. We can, besides, give angle names only with vertices. For example, based on the accompanying image, the angle can be symbolized as ∠BAC, or ∠CAB, or ∠A.  

Note:  

This is one of the classic problems of Euclidean geometry.

Undefined terms are the basic figure that is undefined in terms of other figures. The undefined terms (or primitive terms) in geometry are a point, line, and plane. These key terms cannot be mathematically defined using other known words.

A point represents a location and has no dimension (size). It is marked with a capital letter and a dot.A line represents an infinite number of points extending in opposite directions that have only one dimension. It has one dimension. It is a straight path and no thickness.A plane represents a planar surface that contains many points and lines. A plane extends infinitely in all four directions. It is two-dimensional. Three noncollinear points determine a plane, as there is exactly one plane that can go through these points.    Learn more    What are three collinear points on a line?  Undefined terms are implemented to define a ray Definition of the line segment    

Keywords: the undefined term, is needed to define, an angle, line, point, line, plane, ray, endpoint, acute, obtuse, right, straight, Euclidean geometry

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