Which figure represents an undefined term?

In geometry, undefined terms refer to point, line and plane definitions. Basically, they are the fundamentals to build the rest in Geometry, they are some primitive, their concepts are so intuitive, that there's no actual defintion of them.

So, among the options, we just need to look for a point, a line or a plane. Notice that the last choice is a line, because it has no ending point (the arrows indicate that it's infinite).

Therefore, the last choice, the line, is an undefined term.

Additionally, you may think that the first choice is also an undefined term, but the reason is not is becuase it's a ray, which is defined as a semi-line, which originate in a certain and defined point to the infinte.

MrRoyal MrRoyal · Answer 2 · 2021-09-21T18:02:05+02:00

In plane geometry; a line, a point and a plane are the undefined terms.

The undefined term in from the figure is (d).

From the given figure, we have the following observations

Figure 1 is a ray, because it has an arrow at one of its endpoints
Figure is a line segment because it has two endpoints
Figure 3 has an angle, two rays and two lines segments
Figure 4 is a line because it extends at both ends

From the definition of an undefined term, we can conclude that figure (d) is an undefined term; because it represents a line.