Brian to be a geometry teacher with the Teach for America program and also started the geometry routine at his school




You are watching: Which of the following is an undefined term?

In Geometry, we have several unknown terms: point, line and also plane. From these 3 undefined terms, all other terms in Geometry deserve to be defined. In Geometry, we specify a allude as a location and also no size. A heat is characterized as something the extends infinitely in either direction however has no width and also is one dimensional if a aircraft extends infinitely in 2 dimensions.


There room three undefined state in geometry. From this terms we define everything else. The first term is point. The 2nd term is plane. And the 3rd undefined term is the line. Therefore let's go earlier and define these as much as us can. Now we're no really specifying point, we're just describing it. A allude has no size; the only has a location. And also the way that we label it is with a resources letter. So us can speak to this point P. A airplane is a level surface that has actually no thickness, and also it will prolong infinitely in every direction.So one way to visualize what a airplane could it is in is come think about a paper of paper. Or if there room two differences between a paper of file and a plane, the an initial is this document does not extend in every direction. Secondly, this paper actually has some thickness and also a plane will not. Currently you deserve to name a plane using a single capital letter, commonly written in cursive, or by three non-collinear points. And collinear we'll talk about in a second here, yet collinear means they're no on the very same line. So let's say you had actually a allude right here: allude A, allude B, and allude C. You could call this plane, airplane ABC. An interpretation of coplanar: We actually can specify this, is points, lines, or anything, segments, polygon in the very same plane. So two things are coplanar if they are, as with we have in the photo here, in the very same plane. So "co", you can think of it together a word because that sharing. Therefore you can think the coplanar as sharing the very same plane. Currently the third undefined hatchet is a line. And also a heat is set of points or, words that you could learn later is locus, prolonging in one of two people direction infinitely. So a heat is going come be all the points, and also we deserve to actually choose two of lock to name it. So us can call this line AB. Now when you're labeling a line, it's vital to encompass at least two points. Or if you have actually some sort of smaller letter end here, us can contact this line L. But an alert how I'm creating the arrows over my letters; I have arrows on either side. And also these arrows call you, the geometry student, the it extends infinitely in this direction. Now this arrow here expand infinitely in that direction. You have the right to have points be collinear, that is, lock share the exact same line. So below we could have, C, D, and also E are all collinear. And if friend look at allude F here, I attracted this in to draw a contrast. You have the right to see that allude F is not on this line, so F is no collinear with C, D, and also E. Yet I can say that E is collinear with C and also D, D is collinear v C and also E, and also C is collinear v D and E.

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So the three key terms that room not definable, however only describable, room the line, i beg your pardon is a set of points extending infinitely in one or the other direction; plane, i beg your pardon is a flat surface through no thickness; and the third undefined term is allude and that has actually a location and no size.