A point in geometry is a location. It has no size i.e. no width, no length and no depth.

A point is shown by a dot.

A line is defined as a line of points that extends infinitely in two directions. It has one dimension, length. Points that are on the same line are called collinear points.

A line is defined by two points and is written as shown below with an arrowhead.

Two lines that meet in a point are called intersecting lines.

A part of a line that has defined endpoints is called a line segment. A line segment as the segment between A and B above is written as:

A plane extends infinitely in two dimensions. It has no thickness. An example of a plane is a coordinate plane. A plane is named by three points in the plane that are not on the same line. Here below we see the plane ABC.

A space extends infinitely in all directions and is a set of all points in three dimensions.

You can think of a space as the inside of a box.

Video lesson: Plot a pint, a line, a line segment and an angle in a coordinate plane. To see the solution look at the video in the next page.

Let's talk about four basic definitions, first of all a point. If we want to plot a point on here, it’s simple as just drawing a dot on that location. Example, if we wanted to plot the point -4, 4

we just go to the left 4 and up 4 and then draw a dot in that point. So there's how you plot a point. Next if we want to plot some line you actually need at least two points and you can connect them and then just draw them with an arrow. So if we want to draw the line y = x we can go from the origin up one and over one and then down one and over one as well. So we can say like something like so and it’s important if it's a line to draw your arrows to indicate that it continues forever. So this is a full line, if we want to draw just the line segment we need to distinguish that by having points on the end like so. So if we want to draw a line segment for perhaps from here to here we need to have these points on the end and then we can connect it. Without the arrows we see that this is just a segment between these two points. Finally let's talk about one last thing, an angle; in that case we want to have two lines and we can connect them at some point so one going off, for example, in this direction another angle, another line going off in this direction and that line between them the two lines here make some angle and we denote it by this arc here and that’s it.

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Basic geometry

Basic but to the point