1. ISN NOTES—Math 2/6/13 Circles & Circumference

2. Instructions Write in your Table of Contents the following: -Date: 2/6/13 -Title: Circles & Circumference -Page Number—check what page number you have available next. Each class is different. Make it fit in your notebook. Go to the page number you assigned and draw a horizontal line across the middle to split the page into two sections (Top and Bottom) You will need a second page for continued examples.

3. Draw a horizontal line across the page: _______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________ The top half will be for drawing a circle and labeling its parts and including key concepts. The bottom is for finding the circumference of a circle and a second page will be needed for examples on manipulating the formula.

4. The diameter d is the distance across a circle through its center. The radius r is the distance from the center to any point on a circle. center The circumference C is the distance around a circle. KEY CONCEPT: The circumference C of a circle is equal to its diameter d times , or 2 times its radius r times  C =  d or C = 2  r

5. Examples: 1)Find the circumference of each circle. Use 3.14 for . Round to the nearest tenth if necessary. a) b) C = 2  rC =  d C = 2(3.14)(4)C = (3.14)(63) C = (6.28)(4)C = 197.82 C = 25.12C = 197.8 in C = 25.1 in r = 4 ft d = 63 in

6. 22 can also be used for  7 Examples:Manipulating the formula Find the diameter or radius of each circle. C = 2  rC = 25 ft., diameter = ________ C = 2(22)(21)3 C =  d 725 = 3.14d C = 2(22)(3) 25 = 3.14d C = 132 in3.143.14 8.0 ft = d ______________________________________ C = 30 yd, radius = ________ C = 2  r 30 = 2(3.14)r 30 = 6.28r 6.28 6.28 4.8 yd = r r = 21 in