Chapter 6 Basic Geometric Constructions 177
then provides several ways to complete the
polygon. The following procedure uses the
Edge
option to create an equilateral triangle.
1. Side length AB is given. Refer to
Figure 6-23A.
2. Enter the
Polygon
command. Specify the
number of sides as three.
3. Enter the
Edge
option and select an end-
point. Then, enter the given side length.
If you move the cursor, the triangle is
drawn dynamically in a counterclock-
wise direction. You can enter coordinates
to specify the length and direction of the
edge, or you can use Ortho mode and
direct distance entry.
4. When you specify the endpoint of the
fi rst edge, the triangle is generated
automatically. The resulting triangle is an
equilateral triangle.
Figure 6-23. Constructing an equilateral triangle. A—The given side length. B—The side length is used to draw
a base line. C—A 30°-60° triangle is used to draw the shape based on two given angles (60° angles) and the
included side length. D—A compass is used with the method based on three given side lengths (all three sides
have the same length).
B A
60–
A B C D
Given side
B A B A
C C
B
A
60–
Construct
an Isosceles
Triangle
CAD
An isosceles triangle has two equal sides
and two equal angles, Figure 6-24. In order
to construct an isosceles triangle, one of two
conditions must be given. One condition is all
Figure 6-24. An isosceles triangle has two equal
sides and two equal angles.
Equal
angles
Base
Equal
sides
sides are the same length). The other condi-
tion is two angles and one side length given.
Remember that two of the angles are equal,
so if only one angle is given, you will actually
know two of the angles.
If the length of the two equal sides and the
base are given, construct the triangle with the
method that uses three side lengths described
previously. The manual or CAD method may
be used. Refer to Figure 6-19.
If the two equal angles and one side
length are given, construct the triangle with
the method that uses two angles and the
included side length described previously.
The manual or CAD method may be used.
Refer to Figure 6-21 or Figure 6-22.