Points, Lines, and Planes To understand basic terms of geometry. To understand basic postulates of geometry.

Definitions Point – It is a location in space. A point is represented by a small dot and is named by a capital letter. Space – The set of all points. Line – A series of points that extends in two opposite directions. Collinear points – Points that lie on the same line.

Segment – the part of a line consisting of two end points and all points between them. Ray – the part of a line consisting of one endpoint and all the points of the line on one side of the endpoint. Opposite Rays – two collinear rays with the same endpoint. Opposite rays always form a line.

Example 1 Are points E, F, and C collinear? If so, name the line of which they lie. Are points E, F, and D collinear? If so, name the line of which they lie. n C F m E P D l

Answers Points E, F, and C are collinear. They lie on line m. Points E, F, and D are not collinear. C F m E P D l

Example 1: Naming Segments and Rays Name the segments and rays in the figure at the right. The three segments are LP, PQ, and LQ. The four rays are LP or LQ, PQ, PL, and QP or QL.

Check Understanding Are points F, P, and C collinear? Name line m in 3 other ways.’ Why do you think arrowheads are used when drawing a line or naming a line such as EF? n C F m E P D l

Answers No, not on the same line EF, FC, or CE Arrowheads are used to show that the line extends in opposite directions without end.

More Definitions Plane – It is a flat surface that has no thickness. It contains many lines and extends without end in the direction of all its lines. You can name a plane by either a single capital letter or by at least 3 of its noncollinear points. Coplanar – Points and lines in the same plane are coplanar.

Example 2 Each surface of the ice cube represents part of a plane. Name the plane represented by the front of the ice cube. The front plane can be named by any 3 of these four letters ABFE.

Check Understanding HEF, HEFG, EFG, FGH, and GHE to name a few. List three different names for the plane represented by the top of the ice cube. HEF, HEFG, EFG, FGH, and GHE to name a few.

Basic Postulates of Geometry A postulate or axiom is an accepted statement of fact. You have used some of the following geometry postulates in algebra. For example, you used Postulate 1-1 when you graphed an equation such as y = -2x + 8.You plotted two points and then drew the line through those two points.

Postulate 1-1 Through any two points there is exactly one line. Line t is the only line that passes through points A and B. TWO POINTS DETERMINE A LINE.

Postulate 1-2 If two lines intersect, then they intersect in exactly one point. AE and BD intersect at C. TWO LINES INTERSECT IN A POINT.

Postulate 1-3 If two planes intersect, then they intersect in exactly one line. Plane RST and plane STW intersect in ST. TWO PLANES INTERSECT IN A LINE.

Example 3 They intersect in GF ABFE and BCGF What is the intersection of plane HGFE and plane BCGF? They intersect in GF Check understanding: Name two planes that intersect in BF. ABFE and BCGF

TRIPOD A three-legged stand will always be stable. As long as the feet of the stand don’t lie in one line, the feet of the three legs will lie exactly in one plane

Postulate 1-4 Through any three noncollinear points there is exactly one plane. THREE POINTS DETERMINE A PLANE.

Example 4 Shade the plane that contains A, B, and C. Shade the plane that contains E, H, and C.

Check Understanding a. D b. B Name another point that is in the same plane as points A, B, and C. Name another point that is coplanar with points E, H, and C. a. D b. B

1-2 Quiz The following questions are a review of what we went over today in class. They are designed to help you assess for yourself whether or not you understood today’s lesson. If you do not do well and miss several of the questions it might be a good idea to come in and get some help!

1. Are O, N, and P collinear? If so, name the line on which they lie. Yes, they lie on the line MP. Yes, they lie on the line NP. Yes, they lie on the line MO. No, the three points are not collinear. Non-Response Grid

2. Name the line and plane shown in the diagram. RS and plane RSU Line R and plane RSU RS and plane UR SR and plane UT Non-Response Grid

3. What is the intersection of plane TUYX and plane VUYZ? TX SW UY VZ Non-Response Grid

4. Name a fourth point in plane TUW. Y Z W X Non-Response Grid

5. Plane ABC and plane BCE ____ be the same plane. must may cannot Non-Response Grid

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