9 3 Composite Figures Warm Up Find the

9 -3 Composite Figures Warm Up Find the area of each figure. 1. a rectangle in which b = 14 cm and h = 5 cm A = 70 cm 2 2. a triangle in which b = 6 in. and h = 18 in. A = 54 in 2 3. a trapezoid in which b 1 = 7 ft, b 2 = 11 ft, and h = 3 ft A = 27 ft 2 Holt Geometry

9 -3 Composite Figures Holt Geometry

9 -3 Composite Figures A composite figure is made up of simple shapes, such as triangles, rectangles, trapezoids, and circles. To find the area of a composite figure, find the areas of the simple shapes and then use the Area Addition Postulate. Holt Geometry

9 -3 Composite Figures Find the shaded area of half circle: area of triangle: area of the rectangle: A = bh = 20(14) = 280 mm 2 shaded area: 50 + 280 + 84 ≈ 521. 1 mm 2 Holt Geometry

9 -3 Composite Figures Holt Geometry

9 -3 Composite Figures Example 2: Finding the Areas of Composite Figures by Subtracting Find the shaded area. Round to the nearest tenth, if necessary. area of a triangle: area of the half circle: Subtract the area of the half circle from the area of the triangle. Holt Geometry area of figure: 234 – 10. 125 ≈ 202. 2 ft 2

9 -3 Composite Figures To estimate the area of an irregular shape, you can sometimes use a composite figure. First, draw a composite figure that resembles the irregular shape. Then divide the composite figure into simple shapes. Holt Geometry

9 -3 Composite Figures Check It Out! Example 4 Use a composite figure to estimate the shaded area. The grid has squares with side lengths of 1 ft. Draw a composite figure that approximates the irregular shape. Find the area of each part of the composite figure. Holt Geometry

9 -3 Composite Figures Check It Out! Example 4 Continued area of triangle: area of half circle: area of rectangle: A = lw = (3)(2) = 6 ft 2 The shaded area is about 12 ft 2. Holt Geometry

9 -3 Composite Figures Holt Geometry

9 -3 Composite Figures Lesson Quiz: Part I Find the shaded area. Round to the nearest tenth, if necessary. 1. 2. Holt Geometry 38. 6 cm 2 50 ft 2

9 -3 Composite Figures Lesson Quiz: Part II 3. Mike is remodeling his kitchen. The countertop he wants costs $2. 70 per square foot. How much will Mike have to spend on his remodeling project? $64. 80 Holt Geometry

9 -3 Composite Figures Lesson Quiz: Part III 4. Use a composite figure to estimate the shaded area. The grid has squares with side lengths of 1 cm. about 8. 5 cm 2 Holt Geometry

9 -3 Composite Figures Warm-Up 1. Mike is remodeling his kitchen. The countertop he wants costs $2. 70 per square foot. How much will Mike have to spend on his remodeling project? $64. 80 Holt Geometry