Today I'm going to teach you how to name Geometric Figures, specifically Point line and Plane. A point
is very easy to name they just assign a letter to it. There's point A, there's point B very simple,
but a line is a set of points that is going in opposite directions. Now there's
three points on there, but you use any two points on the line, you can name it line AB,
or you could use a little symbol on top of there, the order doesn't matter it could be BA, AC, CA
BC or AB, any two points, don't use three, don't use one. What about line segments. Well segment
is just a part of a line it, doesn't keep going on forever, so there's no little arrows. Now this
segment here could be called line segment AB or you could just use a little symbol on top of there
and again the order doesn't matter so it could be BA, but you have to name it with those end points.
Now that's going to BC, or CB those two endpoints or the whole line segment
could be AC or CA, just use the end points. Planes can be a little more complicated.
Now here we're going to have a plane, a set of points making up a two-dimensional surface and
see that R right there does not represent a point, we can name the entire plane plane R. It's going
to be cursive if they're going to do that, you could also use any three non-co-linear points
like plane ABC, non-collinear means they don't make a straight line, I'll explain that later
but again the order doesn't matter it could be BAC, or CBA, no big deal. Let's go ahead and try again.
Now this plane could be named plane M, but it also has five little points on there we're going to
use those, go ahead and name it, again that's plane M, here what can we name the plane if all
the arrangements, all the different orders of the same three letters are treated as one name. Well
let's go ahead and just go in order, let's go PQR, it could be named plane PQR just use the symbol
but I'm gonna write all the ways that you could start with just the letter P and I'll go in order,
so we'll go PQS and then PQT, well that's all the ones with PQ so I go to R, PRS
and PRT, using that order makes it much simpler. Well I'm done with R, I move on to S, PST, those
are all the ones that would begin with P. Well what about all the ones that could begin with Q, if I'm
going in order, I'll go QRS and then QRT and then go with the S, I'm done with the R go QST,
so those are all the ones that are left over that begin with Q what about all the ones that begin
with R, if I'm still going in order well, I only have the S and the T left, so so if you go in order
you can find all the different combinations, so now let's get back to that idea of three non-co-linear
points. Why can't I name this plane ABC, well the reason for that, they make a straight line and
you can draw a lot of different planes, an infinite number of planes that will also go through ABC.
Plane N could be called ABC, plane M could be called ABC. I could draw another plane that goes
through it that's ABC, it wouldn't make any sense, so always pick three non-collinear points
and remember that N and M are not points and you have to use three, not four, not two points.