8. Secant
A line that passes through two points of the
circle.
A line that contains a chord.
9. Tangent
A line in the plane of the circle that intersects the
circle in exactly one point.
●
●
The point of contact is called the
Point of Tangency
10. Semicircle
A semicircle is an arc of a circle whose endpoints
are the endpoints of the diameter.
is a semicircle
C
BA
●
ACB
Three letters are
required to name a
semicircle: the
endpoints and one
point it passes through.
11. Minor Arc
An arc of a circle that is smaller than a semicircle.
P
C
B
●
PC or CB are minor arcs
Two letters are required
to name a minor arc:
the endpoints.
12. Major Arc
An arc of a circle that is larger than a semicircle.
C
BA
●
ABC or CAB are major arcs
13. Inscribed Angle
An angle whose vertex lies on a circle and
whose sides contain chords of a circle.
B
A
C
D
<ABC & <BCD are inscribed angles
14. Central Angle
An angle whose vertex is the center of the circle
and sides are radii of the circle.
A
K
B
<AKB is a central angle
15. Properties of Circles
The measure of a central angle is two times the
measure of the inscribed angle that intercepts
the same arc.
P
A
B
C
m<APB = 2 times m<ACB
½ m<APB = m<ACB
x
2x
16. Example
If the m<C is 55°, then the m<O is 110°.
Both angle C and angle O intercept the same arc, AB.
O
A
B
C
55°
110°
17. Angles inscribed in the same arc are congruent.
A
Q
B
P
m<QAP = m<PBQ
Both angles intercept QP
The m<AQB =m<APB
both intercept arc AB.
