Lesson Objectives 1.You will gain a deeper understanding of the concept of circumference. 2.You will demonstrate the proper use of the compass as a device used for drawing circles. 3.You will understand the relationship between the perimeter and the circumference of a circle. 4.You will demonstrate how to measure the circumference on a circle. 5.You will identify the relationship between the diameter and circumference. 6.You will learn to use circumference to solve real- life problems.

Measuring Circumference Developed by Ivan Seneviratne

Drawing a Circle A compass is an instrument used to draw circles; it consists of two pointed arms joined at an adjustable angle.

Circumference The circumference of a circle is the distance around the circle. For all circles, the ratio of the circumference to the diameter is the same. This ratio is known as  or pi. Thus the circumference is little 3 times bigger than the diameter.

Finding the Proof Imagine that the circle is straightening itself out.

C =  × d C =  × 2 x r Theorem The circumference C of a circle is … or where d is the diameter of the circle and r is the radius of the circle. Diameter

Pi or π represents the ratio of any circle's circumference to its diameter. The standard approximation value for pi is 3.14 or 22/7. Standard Value for Pi  = 3.14 or  = 22/7

Find the circumference when the diameter is,,, a)1 cm b)2 cm c)3 cm d)4 cm e)5 cm f)1 m g)2 m h)3 m i)4 m j)5 m Your Turn a)3.14 cm b)6.28 cm c)9.42 cm d)12.56 cm e)15.7 cm f)3.14 m g)6.28 m h)9.42 m i)12.56 m j)15.7 m

Find… (a) the circumference of a circle with radius 6 centimeters and (b) the radius of a circle with circumference 31 meters. Round decimal answers to two decimal places. Using Circumference

This presentation is developed by Ivan Seneviratne © 2007 purely for personal use.