Introduction Geometric figures can be graphed in the coordinate plane, as well as manipulated. However, before sliding and reflecting figures, the definitions.

IntroductionGeometric figures can be graphed in the coordinate plane, as well as manipulated. However, before sliding and reflecting figures, the definitions of some important concepts must be discussed.

Each of the manipulations that will be discussed will move points along a parallel line, a perpendicular line, or a circular arc. In this lesson, each of these paths and their components will be introduced.

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5.1.1: Defining Terms

Key Concepts• A point is not something with dimension; a point is a

“somewhere.” A point is an exact position or location in a given plane. In the coordinate plane, these locations are referred to with an ordered pair (x, y), which tells us where the point is horizontally and vertically. The symbol A (x, y) is used to represent point A at the location (x, y).

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5.1.1: Defining Terms

Key Concepts, continued• A line requires two points to be defined. A line is the

set of points between two reference points and the infinite number of points that continue beyond those two points in either direction. A line is infinite, without beginning or end. This is shown in the diagram below with the use of arrows. The symbol is used to represent line AB.

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5.1.1: Defining Terms

Key Concepts, continued• You can find the linear distance between two points

on a given line. Distance along a line is written as d(PQ) where P and Q are points on a line.

• Like a line, a ray is defined by two points; however, a

ray has only one endpoint. The symbol is used to

represent ray AB.

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5.1.1: Defining Terms

Key Concepts, continued• Similarly, a line segment is also defined by two

points, but both of those points are endpoints. A line segment can be measured because it has two endpoints and finite length. Line segments are used to form geometric figures. The symbol is used to represent line segment AB.

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5.1.1: Defining Terms

Key Concepts, continued• An angle is formed where two line segments or rays share

an endpoint, or where a line intersects with another line, ray, or line segment. The difference in direction of the parts is called the angle. Angles can be measured in degrees or radians. The symbol is use to represent angle A. A represents the vertex of the angle. Sometimes it is necessary to use three letters to avoid confusion. In the diagram below, can be used to represent the same angle, . Notice that A is the vertex of the angle and it will always be listed in between the points on the angle’s rays.

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5.1.1: Defining Terms

Key Concepts, continued• An acute angle measures less than 90° but greater

than 0°. An obtuse angle measures greater than 90° but less than 180°. A right angle measures exactly 90°.

• Two relationships between lines that will help us define transformations are parallel and perpendicular. Parallel lines are two lines that have unique points and never cross. If parallel lines share one point, then they will share every point; in other words, a line is parallel to itself.

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5.1.1: Defining Terms

Key Concepts, continued• Perpendicular lines meet at a right angle (90°),

creating four right angles.

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5.1.1: Defining Terms

Key Concepts, continued• A circle is the set of points on a plane at a certain

distance, or radius, from a single point, the center. Notice that a radius is a line segment. Therefore, if we draw any two radii of a circle, we create an angle where the two radii share a common endpoint, the center of the circle.

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5.1.1: Defining Terms

Key Concepts, continued• Creating an angle inside a circle allows us to define a

circular arc, the set of points along the circle between the endpoints of the radii that are not shared. The arc length, or distance along a circular arc, is dependent on the length of the radius and the angle that creates the arc—the greater the radius or angle, the longer the arc.

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5.1.1: Defining Terms

Common Errors/Misconceptions• mislabeling angles or not including enough points to

specify an angle

• misusing terms and notations

• finding the length of incorrect arcs

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5.1.1: Defining Terms

Guided Practice

Example 4Given the following:

Are and parallel? Are and parallel? Explain.

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5.1.1: Defining Terms

Guided Practice: Example 4, continued

1. and intersect at the same angle and .

will never cross . Therefore, is parallel to .

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5.1.1: Defining Terms

Guided Practice: Example 4, continued

2. and intersect at the same angle, but .

As you move from Z to Y on , you move closer to,

and will eventually intersect, . Therefore, is

not parallel to .

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5.1.1: Defining Terms

✔

Guided Practice: Example 4, continued

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5.1.1: Defining Terms

Guided Practice

Example 5Refer to the figures below. Given , is the set of points with center B a circle? Given , is the set of points with center Y a circle?

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5.1.1: Defining Terms

Guided Practice: Example 5, continued

1. The set of points with center B is a circle because all points are equidistant from the center, B.

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5.1.1: Defining Terms

Guided Practice: Example 5, continued

2. The set of points with center Y is not a circle because the points vary in distance from the center, Y.

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5.1.1: Defining Terms

✔

Guided Practice: Example 5, continued

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5.1.1: Defining Terms