1. Exploring Circles
9.1

2. Warm Up Write the equation of each item. 1. FG 2. EH
3. 2(25 –x) = x + 2
4. 3x + 8 = 4x

3. A circle is the set of all points in a plane that are a given distance from a specific point on that plane.
That specific point is called the center. (You name a circle by it’s center)
Radius: a segment with one endpoint at the center and the other endpoint ON the circle.
Diameter: a segment with endpoints on the circle that passes through the center of the circle. (Diameter = 2 times the radius)

4. Chord: a segment with endpoints on the circle.
Diameter is the largest possible chord.
Secant: a line that intersects a circle in exactly two points. It is an extension of a chord.
Tangent: a line that intersects a circle in exactly one point.

5. Identify each segment

8. Area and Circumference
Area of a circle is the number of square units contained within the circle.
A = π r ^2
Circumference is the distance around a circle.
C = 2 π r or C = π d
Do not use 3.14 for pi, us the π button on your calculator.

9. Name the center of Circle M.
Name a chord that is also a diameter.
If MD = 5 inches, find RI.
Is MI a chord of circle O?
Is MI = MA?
Name 4 radii of circle M.
Is RI > SU?
If RI = 11.8 cm, find MA.
Draw in segment AB. What kind of triangle is triangle MAR?

10. Radius
Diameter
Circumference
Area
5 cm
7 cm
136.9 in2
21.24 cm

11. Find the circumference and area.

12. Find the circumference and area.