1. 9-1 Perimeter and Circumference

2. 9-1 Perimeter and Circumference Warm Up Add or multiply. You need to do BOTH of these! 1. 8.2 + 5.6 + 8.2 + 5.6 2. 22 · 3.14 27.6 69.08

3. 9-1 Perimeter and Circumference Today’s Goal: Learn to find the perimeter of a polygon and the circumference of a circle.

4. 9-1 Perimeter and Circumference Vocabulary perimeter circumference pi

5. 9-1 Perimeter and Circumference Perimeter is the distance around a geometric figure. To find the perimeter P of a polygon, you can add the lengths of its sides.

6. 9-1 Perimeter and Circumference Find the perimeter.-Don’t write this down-just watch! Example 1: Finding the Perimeter of a Polygon 25 cm 15 cm P = 25 + 25 + 15Use the side lengths. P = 65 The perimeter of the triangle is 65 cm. Add.

7. 9-1 Perimeter and Circumference Example 1 20 cm 25 cm 30 cm P = 25 + 20 + 30Use the side lengths. P = 75 The perimeter of the triangle is 75 cm. Add. Find the perimeter of the polygon.- Write this example down!

8. 9-1 Perimeter and Circumference Write this on your formula sheet!

9. 9-1 Perimeter and Circumference Example 2 Find the perimeter of a rectangle.-Don’t write this down-just watch! 16 ft 8 ft P = 2l + 2w P = (2 · 16) + (2 · 8) P = 32 + 16 P = 48 The perimeter of the rectangle is 48 ft. Use the formula. Substitute for l and w. Multiply. Add.

10. 9-1 Perimeter and Circumference Find the perimeter of a rectangle.-Write this down! Using Properties of a Rectangle to Find Perimeter 14 ft 18 ft P = 2l + 2w P = (2 · 18) + (2 ·14) P = 36 + 28 P = 64 The perimeter of the rectangle is 64 ft. Use the formula. Substitute for l and w. Multiply. Add.

11. 9-1 Perimeter and Circumference CdCd 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. CdCd

12. 9-1 Perimeter and Circumference Write this on your formula sheet!

13. 9-1 Perimeter and Circumference Find the circumference of the circle to the nearest tenth. Use 3.14 for .-Write this down! Finding the Circumference of a Circle 12 in. C = d C  3.14 · 12 C  37.68 You know the diameter. Substitute for  and d. Multiply. The circumference of the circle is about 37.7 in.

14. 9-1 Perimeter and Circumference Find the circumference of the circle to the nearest tenth. Use 3.14 for .-Write this down! Finding the Circumference of a Circle 18 cm C = 2r C  2 · 3.14 · 18 C  113.04 You know the radius. Substitute for  and r. Multiply. The circumference of the circle is about 113.0 cm.

15. 9-1 Perimeter and Circumference If the diameter or radius of a circle is a multiple of 7, use for . Helpful Hint 22 7

16. 9-1 Perimeter and Circumference The diameter of a circular spa is 14 m. What is its circumference? Use Example 4 -Just watch this example! 22 7 for . C = d You know the diameter. C  22 7 · 14Substitute 22 7 for  and 14 for d. C  22 7 · 14 1 C  22 7 · 14 1 2 1 C  44 The circumference of the spa is about 44 m. Write 14 as a fraction. Simplify. Multiply.

17. 9-1 Perimeter and Circumference The diameter of a circular pond is 42 m. What is its circumference? Use Application Example -Write this down! 22 7 for . C = d You know the diameter. C  22 7 · 42Substitute 22 7 for  and 42 for d. C  22 7 · 42 1 C  22 7 · 42 1 6 1 C  132 The circumference of the pond is about 132 m. Write 42 as a fraction. Simplify. Multiply.

18. 9-1 Perimeter and Circumference Assignment Page 362 (1-10 all) Page 355 (19-27 odds)