501 Geometry Questions

Adjacent Angles

Adjacent anglesshare a vertex, a side, and no interior points; they are
angles that lie side-by-side.
Because adjacent angles share a single vertex point, adjacent angles can be
added together to make larger angles. This technique will be particularly
useful when working with complementaryand supplementaryangles in
Chapter 5.

Angle and Line Segment Bisectors

The prefix “bi” means “two,” as in bicycle, which has two wheels, or bicen-
tennial, which is a two-hundredth anniversary. In geometry, a bisectoris
any ray or line segment that divides an angle or another line segment into
two congruent and equal parts. Sometimes you will read that a ray “bisects
an angle” and other times a ray may be referred to as an “angle bisector,”
but either way, it means that the ray divides the bisected angle into two
smaller, equal angles. In the following illustration, we can tell that ∠CAK
is bisected by ray AR, since ∠CAR∠RAK. We know these two angles are
congruent because they both have double tick marks in them—when angles
have the same amount of tick marks, it means that they are congruent.

A

R

K

C

Figure 4.3

501 Geometry Questions