Warm Up 1. Find the length of the hypotenuse of a right triangle that has legs 3 in. and 4 in. long. 2. The hypotenuse of a right triangle measures 17 in., and one leg measures 8 in. How long is the other leg? 3. To the nearest centimeter, what is the height of an equilateral triangle with sides 9 cm long? Course Circles 5 in. 15 in. 8 cm
Problem of the Day A rectangular box is 3 ft. by 4 ft. by 12 ft. What is the distance from a top corner to the opposite bottom corner? 13 ft Course Circles
Learn to find the circumference and area of circles. Course Circles TB P
circle radius diameter circumference Vocabulary Course Circles
A circle is the set of points in a plane that are a fixed distance from a given point, called the center. A radius connects the center to any point on the circle, and a diameter connects two points on the circle and passes through the center. Course Circles
Radius Center Diameter Circumference The diameter d is twice the radius r. d = 2r The circumference of a circle is the distance around the circle. Course Circles
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Remember! Pi () is an irrational number that is often approximated by the rational numbers 3.14 and Course Circles
Additional Example 1: Finding the Circumference of a Circle A. Circle with a radius of 4 m C = 2r = 2(4) = 8m 25.1 m B. Circle with a diameter of 3.3 ft C = d = (3.3) = 3.3ft 10.4 ft Find the circumference of each circle, both in terms of and to the nearest tenth. Use 3.14 for . Course Circles
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Additional Example 2: Finding the Area of a Circle A = r 2 = (4 2 ) = 16in 2 50.2 in 2 A. Circle with a radius of 4 in. Find the area of each circle, both in terms of and to the nearest tenth. Use 3.14 for . B. Circle with a diameter of 3.3 m A = r 2 = ( ) = m 2 8.5 m 2 d2d2 = 1.65 Course Circles
Additional Example 3: Finding the Area and Circumference on a Coordinate Plane A = r 2 = (3 2 ) = 9units 2 28.3 units 2 C = d = (6) = 6units 18.8 units Graph the circle with center (–2, 1) that passes through (1, 1). Find the area and circumference, both in terms of and to the nearest tenth. Use 3.14 for Course Circles
Additional Example 4: Measurement Application C = d = (56) 176 ft (56) A Ferris wheel has a diameter of 56 feet and makes 15 revolutions per ride. How far would someone travel during a ride? Use for . Find the circumference The distance is the circumference of the wheel times the number of revolutions, or about 176 15 = 2640 ft. Course Circles
Lesson Quiz Find the circumference of each circle, both in terms of and to the nearest tenth. Use 3.14 for . 1. radius 5.6 m 2. diameter 113 m 11.2 m; 35.2 m 113 mm; mm Find the area of each circle, both in terms of and to the nearest tenth. Use 3.14 for . 3. radius 3 in. 4. diameter 1 ft 9 in 2 ; 28.3 in ft 2 ; 0.8 ft 2 Course Circles