3. Parts of a Circle
Circle – set of all points _________ from a given point called the _____ of the circle (in a plane).
equidistant C
center
Symbol: C

4. CHORD: a segment whose ________ are on the circle

5. RADIUS: distance from the _____ to a point on the circle
center P

6. DIAMETER: distance ______ the circle through its ______
across P
center
Also known as the longest chord.

7. What is the relationship between the diameter and the radius of a circle?OR
D =
½ D
2 r

8. D = ? 24 32 12
r = ? 16
r = ?
4.5 6
D = ? 12 9

9. Use P to determine whether each statement is true or false.Q R T S

10. SECANT sounds like second
Secant Line
A secant line intersects the circle at exactly TWO points.
SECANT sounds like second

11. TANGENT: a LINE that intersects the circle exactly ONE time

12. Point of Tangency

13. Secant Radius Diameter Chord Tangent
Name the term that best describes the line.
Secant
Radius
Diameter
Chord
Tangent

14. Two circles can intersect…
in two points
one point
or no points

15. No points of intersection (different center)

16. No points of intersection (same center)
Concentric Circles
Same center but different radii

17. 1 point of intersection (Tangent Circles)
Externally Tangent
Internally Tangent

18. 2 points of intersection

19. <APB is a Central Angle
Central Angle : An Angle whose vertex is at the center of the circle A
Major Arc
Minor Arc
More than 180°
Less than 180°
ACB P AB
To name: use 3 letters C
To name: use 2 letters B
<APB is a Central Angle

20. Semicircle: An Arc that equals 180°
To name: use 3 letters E D
EDF P F

21. THINGS TO KNOW AND REMEMBER ALWAYS
A circle has 360 degrees
A semicircle has 180 degrees
Vertical Angles are Congruent

22. measure of an arc = measure of central angle
96 Q
m AB =
96° B C
m ACB =
264°
m AE =
84°

23. Arc Addition PostulateB
m ABC =
+ m BC
m AB

24. 240 260 m DAB = m BCA = Tell me the measure of the following arcs. D
140
260
m BCA = R
40
100
80 C B

25. CONGRUENT ARCS
Congruent Arcs have the same measure and MUST come from the same circle or of congruent circles. C B D 45 45
110 A