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Lines and Angles
Planes
A plane is a flat surface that extends indefinitely.
Plane
Space extends in all directions indefinitely.
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
Lines, Segments, and Rays
A
Line AB or AB
B
Line Segment AB or AB
A
B
Ray AB or AB
A
B
Angles
An angle is made up of two rays that share the
same endpoint called the vertex.
A
Vertex
B
x
C
The angle can be named ABC, CBA, B, or x.
The vertex is the
middle point.
Angles
An angle can be measured in degrees. There
are 360º (degrees) in a full revolution or full
circle.
360º
Classifying Angles
Name
Acute Angle
Right Angle
Obtuse
Angle
Straight Angle
Angle Measure
Between 0° and 90°
Exactly 90°
Between 90° and 180°
Exactly 180º
Examples
1
For the figure shown, use symbols to name
a line, two rays, and a segment.
2
In this figure, XY is 12.3 inches and XZ
is 20.1 inches. Find YZ.
A polygon is a flat figure formed by line
segments connected at their ends.
Geometric figures such as triangles, squares,
and rectangles are called polygons.
triangle
square
rectangle
The perimeter of a polygon is the distance
around the polygon.
3
Find the perimeter of this figure. All angles
are right angles. Dimensions are in
centimeters (cm).