1. 1.2 Informal Geometry and Measurement
Undefined terms (terms that are described not defined)
Point:
Represented by a dot
Has location, not size
Has no dimension
Line
Infinite set of points
Have a quality of “straightness”
One-dimensional
Represented symbolically by  (Fig 1.9 p. 10)
Collinear: 3 points on the same line __
Line segment: part of a line between two points: BC
Midpoint: a point equal distance from the ends of a line segment
Plane
Two-dimensional
Infinite number of points and infinite number of lines
Coplanar points: lie in the same plane.
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2. Measuring line segments
Line segment is part of a line consisting of 2 distinct points.
We label a line or line segment by its endpoints.
Fig 1.11 & 1.9 p. 11
Tool: Ruler
Metric conversion: 1 inch = 2.54 cm
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3. Measuring angles Tool: Protractor
Angle’s size depends on the amount of opening between its sides.
Unit of measure: degree
Naming Angles: (Fig 1.10 p. 11)
Where the two sides meet is the vertex.
The vertex is always in the middle with the point on each side surrounding it. ABC .
Ex 4 – 5 p
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4. Relationships Parallel lines, never meet. Figure 1.19 p. 14
Congruent angles have angles of equal measure.
Bisect an angle means to cut the angle in half.
Straight angle has 180 and is a straight line.
Intersecting lines have a point in common.
Perpendicular lines intercept to form two congruent angles. Each is 90.
Right angles are 90.
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5. Circles Fig 1.25 p. 15
Set of all points in a plane that are at a given distance from a particular point (center)
Arc is any part of the circle between any of its two points.
Radius is any line segment joining the center to a point on the circle.
We use a Compass (fig. 1.24) to draw circles or parts of circles (arcs)
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6. Constructions Tools: Compass Straight edge.
Constructions: use ONLY these two tools:
Construct a segment congruent to a given line segment AB. P. 16, Fig. 1.26
Construct the midpoint M of a given line segment AB.
P. 16, Fig 1.27
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