1'2 Informal Geometry and Measurement

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.

2
Measuring line segments

• Tool Ruler
• Metric conversion 1 inch 2.54 cm

3
Measuring angles

• Tool Protractor
• Angles size depends on the amount of opening
  between its sides.
• Unit of measure degree
• Naming Angles (Fig 1.16 p. 13)
• Where the two sides meet is the vertex.
• The vertex is always in the middle with the point
  on each side surrounding it. ?ABC

4
Relationships

• Parallel lines, never meet. Figure 1.19
• Congruent angles have equal angles
• 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?

5
Circles

• 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.

6
Constructions

• Tools
• Compass
• Straight edge.
• Constructions use ONLY these two tools
• Construct a segment congruent to a given line
  segment AB.
• Construct the midpoint M of a given line segment
  AB.