Circumference Formula

8-1 Circumference pt.2

Objectives:

Students will find circumference in terms of pi.

Students will use the circumference formulas to find missing dimensions.

​I Do:

Find the circumference of a circle with a radius of 3.7 meters.

Express your answer in terms of π.

​Think about it!! What does it mean to "Express your answer in terms of π?"

​I Do:

Find the circumference of a circle with a radius of 3.7 meters.

Express your answer in terms of π.

​Think about it!! What does it mean to "Express your answer in terms of π?"

​C = 2πr (write the formula)

C = 2(π)(3.7) (substitute the given number 3.7)

C = 2(3.7)π (rearrange and multiply)

C = 7.4π (just leave the π symbol in your answer)

​It means leave the pi symbol in your answer. Do not put 3.14 into the formula.

​We Do:

Find the circumference of a circle with a radius of 7.5 inches. Express your answer in terms of π.

​You Do:

Find the circumference of a circle with a radius of 21.2 inches. Express your answer in terms of π.

​You Do:

Find the circumference of a circle with a radius of 6.2 meters. Express your answer in terms of π.

​Finding missing dimensions

1. Choose the right formula.

2. Substitute the given values.

3. Solve the equation for the missing dimension.

I Do:

A circle has a circumference of 66 meters.

Find the approximate diameter of the circle. Use 3.14 for π. Round your answer to the nearest hundredth.

I Do:

A circle has a circumference of 66 meters.

Find the approximate diameter of the circle. Use 3.14 for π. Round your answer to the nearest hundredth.

1. ​C = πd (Write the formula)

2. 66 = 3.14d (substitute the given numbers)

3. 66/3.14 = 3.14d/3.14 (divide to solve the equation)

4. 21.01910 = d

5. 21.02 = d (rounded to the nearest hundredth)

We Do:

A circle has a circumference of 70.82 meters.

Find the approximate radius of the circle. Use 3.14 for π. Round your answer to the nearest hundredth.

You Do Together:

The world’s largest flower, the Rafflesia, has a circumference of 286 centimeters. Find the approximate diameter of the flower. Use 3.14 for π. Round to the nearest hundredth if necessary.

You Do Together:

Find the approximate radius of a circle with a circumference of 34.48 inches. Use 3.14 for π. Round to the nearest hundredth.