Draw a straight line, mark points A and B on it, and mark point C on the segment AB.

Draw a straight line, mark points A and B on it, and mark point C on the segment AB. Name the ray, which is a continuation of the CA ray.

In the problem, you need to draw a straight line and mark on it two non-coinciding points A and B. Take point C, which lies on the segment [AB].

To solve the problem, it is necessary to name the ray, which is a continuation of the ray [CA).

The concept of a straight line and a ray
A straight line in geometry is understood as an endless line that does not bend. This means that if you take two mismatched points on a straight line, then the path along that line is the distance (or shortest distance) between these points. In other words, if there are two points, then the line is that line, the path along which from one point to the second is the shortest of all possible. A straight line has no beginning or end, and continues indefinitely in two directions. A straight line passing through two points A and B is usually denoted as (AB).

A ray in geometry is a part of a straight line that has a fixed beginning, but has no end. For example, if a ray has its origin at point A and passes through point B, then it is usually denoted as [AB). If the ray starts at point B and passes through point A, then it will be denoted as [BA).

Beam Continuation [CA)
In this problem, the line (AB) is divided by point C into two rays [CA) and [CB). For both of these rays, point C is the beginning. An extension of the ray [CA) is a ray that:

has the same origin, i.e. point C;
lies together with the ray [CA) on one straight line, i.e. on a straight line (AB);
does not coincide with the beam [CA).
Obviously, only the ray [CB] satisfies all these conditions.

Answer: the extension of the ray [SA) is the ray [CB)

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