1. Circle Vocabulary

2. Circle – set of all points _________ from a given point called the _____ of the circle.
equidistant C
center
Symbol: C

3. CHORD:
A segment whose endpoints are on the circle

4. DIAMETER: Distance across the circle through its centerP
Also known as the longest chord.

5. RADIUS:
Distance from the center to point on circle P

6. Radius = ½ diameter or Diameter = 2r
Formula
Radius = ½ diameter or
Diameter = 2r

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

8. Use P to determine whether each statement is true or false.Q R T S
True: thumbs up False: thumbs down

9. Secant Line:
intersects the circle at exactly TWO points

10. Tangent Line: a LINE that intersects the circle exactly ONE time
Forms a 90°angle with one radius
Point of Tangency: The point where the tangent intersects the circle

11. Secant Radius Diameter Chord Tangent
Name the term that best describes the notation.
Secant
Radius
Diameter
Chord
Tangent

12. An angle whose vertex is at the center of the circle
Central Angles
An angle whose vertex is at the center of the circle

13. 3 Types of Arcs Minor Arc ACB AB Major Arc APB is a Central Angle
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

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

15. THINGS TO KNOW AND REMEMBER ALWAYS
A circle has 360 degrees
A semicircle has 180 degrees
Vertical Angles are CONGRUENT
Linear Pairs are SUPPLEMENTARY

16. Formula measure Arc = measure Central Angle

17. Find the measures. EB is a diameter.C Q
96 E
m AB =
96°
m ACB =
264°
m AE =
84°

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

19. 240 260 m DAB = m BCA = Tell me the measure of the following arcs.
AC is a diameter. D A
m DAB =
140
240 R
40
100
80
260
m BCA = C B

20. Congruent Arcs have the same measure and MUST come from the same circle or of congruent circles.B D 45 45
110 A
Arc length is proportional to “r”

21. Textbook
p #11
p #11 – 16, 25 – 30, 38