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## Geometry and Measurement

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### Chapter Nine Geometry and Measurement Lines and Angles Section 9.1 Plane A plane is a flat surface that extends indefinitely. Space extends in all directions ... – PowerPoint PPT presentation

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Title: Geometry and Measurement

1
Geometry and Measurement
Chapter Nine
2
Lines and Angles
Section 9.1
3
A plane is a flat surface that extends
indefinitely.
Plane
Space extends in all directions indefinitely.
Martin-Gay, Prealgebra, 5ed
4
Point
The most basic concept of geometry is the idea of
a point in space. A point has no length, no
width, and no height, but it does have location.
We will represent a point by a dot, and we will
label points with letters.
A
Point A
Martin-Gay, Prealgebra, 5ed
5
A
B
A
B
A
B
Martin-Gay, Prealgebra, 5ed
6
An angle is made up of two rays that share the
same endpoint called a vertex.
Vertex
The angle can be named ?ABC, ?CBA, ?B, or ?x.
7
An angle can be measured in degrees. There are
360º (degrees) in a full revolution or full
circle.
360º
Martin-Gay, Prealgebra, 5ed
8
Classifying Angles
Name
Angle Measure
Examples
Acute Angle
Between 0 and 90
Right Angle
Exactly 90
Obtuse Angle
Between 90 and 180
Straight Angle
Exactly 180º
9
Two angles that have a sum of 90 are called
complementary angles.
Two angles that have a sum of 180 are called
supplementary angles.
Martin-Gay, Prealgebra, 5ed
10
Two lines in a plane can be either parallel or
intersecting. Parallel lines never meet.
Intersecting lines meet at a point. The symbol
?? is used to denote is parallel to.
Parallel lines
Intersecting lines
p ?? q
Martin-Gay, Prealgebra, 5ed
11
Two lines are perpendicular if they form right
angles when they intersect. The symbol ? is
used to denote is perpendicular to.
Perpendicular lines
n ? m
Martin-Gay, Prealgebra, 5ed
12
When two lines intersect, four angles are formed.
Two of these angles that are opposite each other
are called vertical angles. Vertical angles have
the same measure.
Martin-Gay, Prealgebra, 5ed
13
Two angles that share a common side are called
intersecting lines are supplementary. That is,
they have a sum of 180 .
?a and ?b
?b and ?c
?c and ?d
?d and ?a
Martin-Gay, Prealgebra, 5ed
14
A line that intersects two or more lines at
different points is called a transversal.
Martin-Gay, Prealgebra, 5ed
15
Parallel Lines Cut by a Transversal
• If two parallel lines are cut by a transversal,
then the measures of corresponding angles are
equal and alternate interior angles are equal.

Martin-Gay, Prealgebra, 5ed
16
Corresponding angles are equal.
Martin-Gay, Prealgebra, 5ed
17
Alternate interior angles are angles on opposite
sides of the transversal between the two parallel
lines.
Martin-Gay, Prealgebra, 5ed