1. CIRCLES OBJECTIVE:
Learn the basic terminology for circles and lines and segments associated with circles.

2. CIRCLES
A circle is
THE SET OF ALL POINTS IN A PLANE THAT ARE EQUIDISTANT FROM A GIVEN POINT, CALLED THE CENTER.
A circle is named by its
center. P

3. CIRCLES Points inside the circle form the circle’s interior.
Points outside the circle form the circle’s exterior.
Exterior
Interior

4. CIRCLES
A radius is . . .
A SEGMENT FROM THE CENTER TO A POINT ON THE EDGE OF THE CIRCLE.
All radii are congruent.
The length of the segment is also called the radius.

5. CIRCLES
A diameter is . . .
A LINE SEGMENT CONTAINING THE CENTER OF THE CIRCLE WITH ITS ENDPOINTS ON THE CIRCLE.
The length of the segment is also called the diameter.

6. CIRCLES
CONGRUENT CIRCLES
HAVE THE SAME
RADII

7. TWO OR MORE COPLANAR CIRCLES THAT HAVE THE SAME
CONCENTRIC CIRCLES
TWO OR MORE COPLANAR CIRCLES THAT HAVE THE SAME
CENTER

8. CIRCLES
An arc is . . .
TWO POINTS ON A CIRCLE AND THE CONTINUOUS (UNBROKEN) PART OF THE CIRCLE BETWEEN THE POINTS.

9. CIRCLES A semicircle is . . .
AN ARC WHOSE ENDPOINTS ARE THE ENDPOINTS OF A DIAMETER.
A HALF-CIRCLE.

10. CIRCLES Minor arcs are . . . SMALLER THAN SEMICIRCLES.
Major arcs are . . .
LARGER THAN SEMICIRCLES.

11. CIRCLES A B C D

12. CIRCLES A B C D

13. CIRCLES A B C D

14. Arcs are measured in degrees.
CIRCLES
Arcs are measured in degrees.
A full circle measures
3600 A B

15. CIRCLES A central angle is . . .
AN ANGLE WITH ITS VERTEX AT THE CENTER OF A CIRCLE AND SIDES PASSING THROUGH THE ENDPOINTS OF AN ARC.

16. CIRCLES
CENTRAL
ANGLE

17. CIRCLES
The measure of an arc is the same as the measure of its CENTRAL ANGLE.

18. ARC ADDITION POSTULATE
CIRCLES
ARC ADDITION POSTULATE
The measure of an arc formed by two adjacent arcs is the sum of the measures of the two arcs.

19. ARC ADDITION POSTULATEB C

20. CIRCLES
A chord is . . .
A LINE SEGMENT WHOSE ENDPOINTS LIE ON THE CIRCLE.

21. CIRCLES
A tangent is . . .
A LINE THAT INTERSECTS THE CIRCLE ONLY ONCE.
The point where the tangent intersects the circle is the
POINT OF TANGENCY

22. CIRCLES
A secant is . . .
A LINE THAT INTERSECTS A CIRCLE AT TWO POINTS.

23. CIRCLES INSCRIBED CIRCLES
A circle is inscribed in a polygon if each side of the polygon is tangent to the circle.

24. CIRCUMSCRIBED CIRCLES
A circle is circumscribed about a polygon if each vertex of the polygon lies on the circle.

25. CIRCLES
COMMON TANGENTS

26. CIRCLES Common tangents are lines that are tangent to two circles.
A common tangent that does not intersect the segment that joins the centers of the circles is a common external tangent.
A common tangent that intersects the segment that joins the centers is a common internal tangent.