Geometry

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Mathematics Geometry Geometry

	Geometry
	In geometry there are only four imaginary items—simple ideas—upon which everything else is built: point, line, plane, and space. The interesting thing about a point is that it has no dimensions—no length, no width, no depth. It is simply a location. We use a dot, like point N shown here, to symbolize a point. A line is a set of points that has only one dimension, length. Points on the same line are called "collinear points." Two points are needed to define a line. The arrowheads on line DE show us that the line extends endlessly in both directions - it has no endpoints. When two lines meet at a point, they are called "intersecting lines." 0 The set of points called a plane lies all on one surface. A plane actually extends endlessly. Also, remember that the surface of a plane has no thickness. At least three points not on the same line are needed to define a plane. At last, there is space, the set of all points. It's difficult to illustrate the idea of space. You can think of it as an open, empty room, or the inside of an empty box. Space has no boundaries and extends endlessly in all directions. Line segment A line segment is simply a part of a line that has a specific length and specific endpoints. denotes the line segment AB. Ray A ray is a part of a line that has only one endpoint. It extends endlessly in one direction. Notice the symbol for a ray. Angle Two rays joined with a common endpoint form an angle. The common endpoint is called a vertex.