Points, Lines, and PlanesLesson 2a

C B

A

l R

S

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I. PointA. Has no size--think of a dot ()B. Named and labeled by capital letters

Examples: A

C B

Definitions:

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II. LineA. Has an infinite set of pointsB. Has no thicknessC. A line is named by a lower case letter or by

any 2 points on the line.

l A

B

D. The double arrow indicates that theline continues without end in both directions.

line l or AB

DefinitionsCont. . . .

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III. Line SegmentA. A part of a line consisting of two

endpoints and all the points between them.

B. In drawings, line segments are usually named with capital letters representing the endpoints.

C. For example, the line segment above could be named Segment AB or AB.

A B

DefinitionsCont. . . .

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IV. PlaneA. A plane is also an infinite set of points.B. Think of flatness as suggested by a table

top extending in all directions without boundaries.

C. Also has no thickness.D. Named and labeled by a capital letter - -

or by three points not on the same line.

DefinitionsCont. . . .

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V. Space is the set of all points.

VI. Collinear points are points that lie on the same line.Noncollinear points are points that do not lie on the same line.

VII. Coplanar points are points that lie on the same plane.

Noncoplanar points are points that do not lie on the same plane.

DefinitionsCont. . . .

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Are the following sets of points coplaner?

1. B,C,G,F2. B,C,D,F3. A,C,G,E4. E,F,G,H

YES or NOYES or NOYES or NOYES or NO

Practice:

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•V

Practice:

Are the following sets of points collinear?

1. S,T,Q2. S,T,V3. T,R,Q4. U,R,T

•U

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YES or NOYES or NOYES or NOYES or NO