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## Points, Lines, and Planes

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**Points, Lines, and Planes**Geometry Mrs. King Unit 1, Lesson 2**A**P Q Z Definition Point: a location in space. A point has no size, but is represented by a dot labeled with a capital letter.**Definition**Space: the set of all points**l**Q P Definition Line: a series of points that extends without end in two opposite directions.**Q**R P Definition Collinear: points that lie on the same line.**In the figure below, name three points that are collinear**and three points that are not collinear. Practice Points Y, Z, and W lie on a line, so they are collinear. For example, X, Y, and Z and X, W, and Z form triangles and are not collinear.**Definition**Plane: a flat surface that extends in all directions without end.**Practice**Name the plane shown in two different ways. You can name a plane using any three or more points on that plane that are not collinear. Some possible names for the plane shown are: plane RST plane RSU plane RTU plane STU plane RSTU**Definition**Coplanar: points and lines that are in the same plane.**Practice**• How many planes are represented by the surfaces of the cube? • Name the plane of the front of the cube in two different ways. • Name a point that is coplanar with the given points: • E, F, G • B, C, G**Definition**Postulate: an accepted statement of fact.**Four Basic Postulates**1-1: Through any two points there is exactly one line. 1-2: If two lines intersect, then they intersect in exactly one point. 1-3: If two planes intersect, then they intersect in a line. 1-4: Through any three noncollinear points there is exactly one plane.**Homework**Points, Lines, and Planes in Student Practice Packet (Page 3, #1-21)