9-1 Perimeter and Circumference
9-1 Perimeter and Circumference Warm Up Add or multiply. You need to do BOTH of these! ·
9-1 Perimeter and Circumference Today’s Goal: Learn to find the perimeter of a polygon and the circumference of a circle.
9-1 Perimeter and Circumference Vocabulary perimeter circumference pi
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.
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 = Use the side lengths. P = 65 The perimeter of the triangle is 65 cm. Add.
9-1 Perimeter and Circumference Example 1 20 cm 25 cm 30 cm P = Use the side lengths. P = 75 The perimeter of the triangle is 75 cm. Add. Find the perimeter of the polygon.- Write this example down!
9-1 Perimeter and Circumference Write this on your formula sheet!
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 = P = 48 The perimeter of the rectangle is 48 ft. Use the formula. Substitute for l and w. Multiply. Add.
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 = P = 64 The perimeter of the rectangle is 64 ft. Use the formula. Substitute for l and w. Multiply. Add.
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
9-1 Perimeter and Circumference Write this on your formula sheet!
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 You know the diameter. Substitute for and d. Multiply. The circumference of the circle is about 37.7 in.
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 = 2r C 2 · 3.14 · 18 C You know the radius. Substitute for and r. Multiply. The circumference of the circle is about cm.
9-1 Perimeter and Circumference If the diameter or radius of a circle is a multiple of 7, use for . Helpful Hint 22 7
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 · C 44 The circumference of the spa is about 44 m. Write 14 as a fraction. Simplify. Multiply.
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 · C 132 The circumference of the pond is about 132 m. Write 42 as a fraction. Simplify. Multiply.
9-1 Perimeter and Circumference Assignment Page 362 (1-10 all) Page 355 (19-27 odds)