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The ratio of the circumference to the diameter of a circle is a special number in mathematics. It is called pi (pronounced “pie”). The symbol for pi is the Greek letter 
.
.
Historical Note
is a nonrepeating decimal that goes on and on forever. One of the earliest good estimates for was made by a famous Greek mathematician named Archimedes in about 240 bce. Archimedes' estimate for was correct to two decimal places (3.14). Today, mathematicians, with the help of computers, have accurately calculated to billions of decimal places.
- Copy the table at the right and find the missing values. Use the
key on your
calculator and round your answers to the nearest hundredth. - Write a number sentence using C and D that tells how to find the diameter of a circle if the circumference is known. This kind of number sentence is called a formula.
- Write a formula using C and D that tells how to find the circumference of a circle if the diameter is known.
- The diameter of a circle is 20 cm.
- Estimate the circumference using 3 for .
- Use paper and pencil and 3.14 for to get a better estimate of the circumference.
- Use your calculator and the key. Compare your answers.
