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. 12/30/2018

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 12/30/2018

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. 14-15 12/30/2018

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. 12/30/2018

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) 12/30/2018

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 12/30/2018