Perimeter and Circumference

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Perimeter and Circumference Course 2 9-2 Perimeter and Circumference Problem of the Day- Warm Up 437 tiles

Perimeter and Circumference Course 2 9-2 Perimeter and Circumference C d The distance around a circle is called circumference. For every circle, the ratio of circumference C to diameter d is the same. This ratio, , is represented by the Greek letter , called pi. Pi is approximately equal to 3.14 or . By solving the 22 7 equation =  for C, you get the formula for circumference. the formula for circumference. C = d, or C = 2r. Copy first sentence and the 3 equations in the last 3 lines. http://www.youtube.com/watch?v=1XFkAZW-rWg

CIRCUMFERENCE OF A CIRCLE Course 2 9-2 Perimeter and Circumference CIRCUMFERENCE OF A CIRCLE The circumference C of a circle is  times the diameter d, or 2 times the radius r. Radius C = d, or C = 2r Diameter Copy the last column of the picture of a circle with the 3 parts labeled (radius, diameter, circumference) Circumference

Additional Example 3A: Finding the Circumference of a Circle Course 2 9-2 Perimeter and Circumference Additional Example 3A: Finding the Circumference of a Circle Find the circumference of the circle to the nearest tenth. Use 3.14 for . C = d You know the diameter. 12 in. C  3.14 · 12 Substitute for  and d. C  37.68 Multiply. Copy into notes The circumference of the circle is about 37.7 in.

Additional Example 3B: Finding the Circumference of a Circle Course 2 9-2 Perimeter and Circumference Additional Example 3B: Finding the Circumference of a Circle Find the circumference of the circle to the nearest tenth. Use 3.14 for . C = 2r You know the radius. 18 cm C  2 · 3.14 · 18 Substitute for  and r. C  113.04 Multiply. Copy into notes The circumference of the circle is about 113.0 cm.

Perimeter and Circumference Course 2 9-2 Perimeter and Circumference Check It Out: Example 3A Find the circumference of the circle to the nearest tenth. Use 3.14 for . C = d You know the diameter. 7 in. C  3.14 · 7 Substitute for  and d. C  21.98 Multiply. Copy into notes The circumference of the circle is about 22.0 in.

Perimeter and Circumference Course 2 9-2 Perimeter and Circumference Check It Out: Example 3B Find the circumference of the circle to the nearest tenth. Use 3.14 for . C = 2r You know the radius. 11 cm C  2 · 3.14 · 11 Substitute for  and r. C  69.08 Multiply. The circumference of the circle is about 69.1 cm.

Perimeter and Circumference Course 2 9-2 Perimeter and Circumference If the diameter or radius of a circle is a multiple of 7, use for p. Helpful Hint 22 7 Copy into notes

Additional Example 4: Application Course 2 9-2 Perimeter and Circumference Additional Example 4: Application The diameter of a circular pond is 42 m. What is its circumference? Use for . 22 7 C = d You know the diameter. 22 7 22 7 C  · 42 Substitute for  and 42 for d. 22 7 42 1 C  · Write 42 as a fraction. 6 Copy into notes 22 7 42 1 · C  Simplify. 1 C  132 Multiply. The circumference of the pond is about 132 m.

Perimeter and Circumference Course 2 9-2 Perimeter and Circumference Check It Out: Example 4 The diameter of a circular spa is 14 m. What is its circumference? Use 22 7 for . C = d You know the diameter. 22 7 22 7 C  · 14 Substitute for  and 14 for d. 22 7 14 1 C  · Write 14 as a fraction. 2 22 7 14 1 · C  Simplify. 1 C  44 Multiply. The circumference of the spa is about 44 m.