1. Opening Activity 1. What is the area of a rectangle with a length of 5 inches and a width of 12 inches? (Remember: A=lw) A=lw A=(5)(12) 2. What is the area of a triangle with a base of 2 cm and a height of 14 cm? Remember: Please clear off your desks except for homework, opening activity, and a calculator!

2. Chapter 8 Lesson1 Circumference

3. Objective: Students will find the circumference of circles.

4. The Circumference of a circle is the distance around a circle. The diameter is the distance across a circle through it’s center. The radius is the distance from the center to any point on the circle. center diameter radius

5. The diameter d of a circle is twice its radius r. The radius of r of a circle is half of its diameter d. d=2r Example 1: Find the radius when d= 23 cm 23 divided by 2 = 11.5 r=11.5 cm

6. Example 2: Find the radius when d=16 yd r= 8 yd Example 3: Find the diameter when r = 3 in d=2r d= 2(3) Diamter= 2 times 3 d= 6 in

7. Example 4: Find diameter when r=5.2 cm d=2r d=2(5.2) d=10.4 cm

8. The circumference of a circle is equal to pi times its diameter or pi times twice its radius. Remember that pi=3.14. Example 5: Find the circumference of the circle. 70 in C=219.8 in

9. Example 6: Find the circumference of the circle. 8 ft C= 2(3.14)(8) C= 50.24 ft

10. Example 7: John is making a circular table that has a top with a diameter of 24 inches. Find the circumference of the table. Round to the nearest tenth. 24 in Draw a picture. C=3.14(24) C=75.36 Round to the tenths place (One place after the decimal.) C=75.4 in