10-1 Finding Perimeter Course 1 Warm Up Warm Up Lesson Presentation Lesson Presentation Problem of the Day Problem of the Day

Learn to find the perimeter and missing side lengths of a polygon. Course Finding Perimeter

Vocabulary perimeter Insert Lesson Title Here Course Finding Perimeter

The perimeter of a figure is the distance around it. To find the perimeter you can add the lengths of the sides. Course Finding Perimeter

Additional Example 1: Finding the Perimeter of a Polygon Find the perimeter of the figure Add all the side lengths. The perimeter is 17.2 in. Course Finding Perimeter

Try This: Example 1 Find the perimeter of the figure Add all the side lengths. 3.3 in. 4.2 in. 3 in. The perimeter is 18 in. Course Finding Perimeter

Course Finding Perimeter

Additional Example 2: Using a Formula to Find Perimeter Find the perimeter P of the rectangle. P = 2l+ 2w Substitute 12 for l and 3 for w. P = (2 12) + (2 3) P = P = 30 Multiply. Add. The perimeter is 30 cm. 12 cm 3 cm Course Finding Perimeter

Try This: Example 2 Find the perimeter P of the rectangle. P = 2l + 2w Substitute 15 for l and 2 for w. P = (2 15) + (2 2) P = P = 34 Multiply. Add. The perimeter is 34 cm. 15 cm 2 cm Course Finding Perimeter

A. What is the length of side a if the perimeter equals 1,471 mm? P = sum of side lengths Use the values you know. 1,471 = a 1,471 = 1,178 + a 1,471 – 1,178 = 1,178 + a – 1,178 Add the known lengths. Subtract 1,178 from both sides. 293 = a Side a is 293 mm long. Additional Example 3A: Finding Unknown Side Lengths and the Perimeter of a Polygon Find each unknown measure. Course Finding Perimeter

Additional Example 3B: Finding Unknown Side Lengths and the Perimeter of a Polygon Find each unknown measure. B. What is the perimeter of the polygon? First find the unknown side length. Find the sides opposite side b. The length of side b = Side b is 72 cm long. P = P = 254 Find the perimeter. The perimeter of the polygon is 254 cm. Course Finding Perimeter 72 cm

l = 4w Find the length. l = (4 19) l = 76 Substitute 19 for w. Multiply. Additional Example 3C: Finding Unknown Side Lengths and the Perimeter of a Polygon C. The width of a rectangle is 19 cm. What is the perimeter of the rectangle if the length is 4 times the width? 4w4w 19 cm Course Finding Perimeter

Additional Example 3C Continued P = 2 l + 2 w Substitute 76 and 19. P = 2(76) + 2 (19) P = P = 190 Multiply. Add. Use the formula for the perimeter of a rectangle. The perimeter of the rectangle is 190 cm. 4w4w 19 cm Course Finding Perimeter

Try This: Example 3A Find each unknown measure. A. What is the length of side a if the perimeter equals 1,302 mm? P = sum of side lengths Use the values you know. 1,302 = a 1,302 = a 1,302 – 982 = a – 982 Add the known lengths. Subtract 982 from both sides. 320 = a Side a is 320 mm long. 212 mm280 mm a 250 mm 240 mm Course Finding Perimeter

First find the unknown side length. Find the sides opposite side b. The length of side b = Side b is 16 m long. P = P = 60 Find the perimeter. The perimeter of the polygon is 60 m. Try This: Example 3B Find each unknown measure. B. What is the perimeter of the polygon? 12 m 14 m b m 8 m 6 m 4 m 16 m Course Finding Perimeter

l = 5w Find the length. l = (5 13) l = 65 Substitute 13 for w. Multiply. Try This: Example 3C C. The width of a rectangle is 13 cm. What is the perimeter of the rectangle if the length is 5 times the width? 5w5w 13 cm Course Finding Perimeter

Try This: Example 3C Continued 65 cm 13 cm P = 2 l + 2 w Substitute 65 and 13. P = 2(65) + 2 (13) P = P = 156 Multiply. Add. Use the formula for the perimeter of a rectangle. The perimeter of the rectangle is 156 cm. Course Finding Perimeter

Lesson Quiz Find each perimeter What is the perimeter of a polygon with side lengths of 15 cm, 18 cm, 21 cm, 32 cm, and 26 cm? 4. What is the perimeter of a rectangle with length 22 cm and width 8 cm? 9 cm 4 ft Insert Lesson Title Here 112 cm 60 cm 5 6 __ Course Finding Perimeter