1. Circles, Circumference, and Area Section 10-1

2. Circle: Definition: A circle is the locus of points in a plane that are a fixed distance from a point called the center of the circle.  A has radius r = AB and diameter d = CD.

5. Lesson Quiz: Part I 1. Identify each line or segment that intersects  Q. chords VT and WR secant: VT tangent: s diam.: WR radii: QW and QR

6. Measure the circumference and diameter of a circle and divide the circumference by diameter CircumferenceDiameterC/D

7. Cirmumference C = πd

8. Example: A drum kit contains three drums with diameters of 10 in., 12 in., and 14 in. Find the circumference of each drum. 10 in. diameter 12 in. diameter 14 in. diameter C = d C = (10)C = (12)C = (14) C = 31.4 in.C = 37.7 in.C = 44.0 in.

9. You can use the circumference of a circle to find its area. Divide the circle and rearrange the pieces to make a shape that resembles a parallelogram. The base of the parallelogram is about half the circumference, or r, and the height is close to the radius r. So A   r · r =  r 2. The more pieces you divide the circle into, the more accurate the estimate will be.

10. Area of a Circle: A = πr 2 Find the area of the circle if its diameter is 10. Find the area of the circle if its circumference is 8π.