58 CNC Machining
Radius
M
N T
S
Q
R
J
K
K
L
Diameter Circumference
Arc Chord Tangent
Figure 3-7. Illustrations of various terms relating to a circle.
The circumference is the distance around a circle.
A chord is a segment that joins any two points on the circumference of
a circle.
An arc is a curved portion of a circle.
A tangent to a circle is a line that intersects a circle at a single point.
For example, as shown in Figure 3-7, Line L is tangent to the circle and
intersects the circle at Point K.
Propositions
A proposition is a statement to be proved, explained, or discussed.
Following are a number of geometric propositions.
• Opposite angles are equal. When two lines intersect, they form equal
angles. Thus, in Figure 3-8, Angle 1 equals Angle 3, and Angle 2
equals Angle 4.
• Two angles are equal if they have parallel corresponding sides.
Thus, in Figure 3-9, Angle 1 equals Angle 2.
• A line perpendicular to one of two parallel lines is perpendicular to
the other line. Thus, in Figure 3-10, Lines R and S are perpendicular
to Line T.
1
3
2 4
Figure 3-8. Two intersecting lines form four angles with the opposite angles being
equal.