# 9-3 Composite Figures Warm Up Find the area 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 cm2 2. a triangle in which b = 6 in. and h = 18 in. A = 54 in2 3. a trapezoid in which b1 = 7 ft, b2 = 11 ft, and h = 3 ft A = 27 ft2 Holt Geometry

9-3 Composite Figures Objectives Use the Area Addition Postulate to find the areas of composite figures. Use composite figures to estimate the areas of irregular shapes. 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 Example 1A: Finding the Areas of Composite Figures by Adding Find the shaded area. Round to the nearest tenth, if necessary. Divide the figure into parts.

area of half circle: Holt Geometry 9-3 Composite Figures Example 1A Continued area of triangle: area of the rectangle: A = bh = 20(14) = 280 mm2 shaded area: 50 + 280 + 84 521.1 mm2

Holt Geometry 9-3 Composite Figures Example 1B: Finding the Areas of Composite Figures by Adding Find the shaded area. Round to the nearest tenth, if necessary. Divide the figure into parts. area of parallelogram: A = bh = 8(5)= 40ft2 area of triangle:

shaded area: 40 + 25 = 65 ft2 Holt Geometry 9-3 Composite Figures Check It Out! Example 1 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 ft2 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 circle:

A = r2 = (10)2 = 100 cm2 area of trapezoid: area of figure: 100 128 186.2 cm2 Holt Geometry 9-3 Composite Figures Check It Out! Example 2 Find the shaded area. Round to the nearest tenth, if necessary. area of circle: A = r2 = (3)2 28.3 in2 area of square:

A = bh (4.24)(4.24) 18 in2 area of figure: 28.3 18 = 10.3 in2 Holt Geometry 9-3 Composite Figures Example 3: Fabric Application A company receives an order for 65 pieces of fabric in the given shape. Each piece is to be dyed red. To dye 6 in2 of fabric, 2 oz of dye is needed. How much dye is needed for the entire order? To find the area of the shape in square inches, divide the

shape into parts. The two half circles have the same area as one circle. Holt Geometry 9-3 Composite Figures Example 3 Continued The area of the circle is (1.5)2 = 2.25 in2. The area of the square is (3)2 = 9 in2. The total area of the shape is 2.25 + 9 16.1 in2.

The total area of the 65 pieces is 65(16.1) 1044.5 in2. The company will need 1044.5 for the entire order. Holt Geometry 348 oz of dye 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 Example 4: Estimating Areas of Irregular Shapes Use a composite figure to estimate the shaded area. The grid has squares with a side length of 1 ft. Draw a composite figure that approximates the irregular

shape. Find the area of each part of the composite figure. a Holt Geometry d b c 9-3 Composite Figures Example 4 Continued

area of triangle a: d b c area of triangle b: a area of rectangle c: A = bh = (2)(1) = 2 ft2 area of trapezoid d:

Area of composite figure: 1 + 0.5 + 2 + 1.5 = 5 ft2 The shaded area is about 5 ft2. 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 ft2 The shaded area is about 12 ft2.

Holt Geometry 9-3 Composite Figures Example 1A: Estimating Areas of Irregular Shapes in the Coordinate Plane Estimate the area of the irregular shape. Holt Geometry 9-3 Composite Figures Example 1A Continued Method 1: Draw a composite

figure that approximates the irregular shape and find the area of the composite figure. The area is approximately 4 + 5.5 + 2 + 3 + 3 + 4 + 1.5 + 1 + 6 = 30 units2. Holt Geometry 9-3 Composite Figures Example 1A Continued Method 2: Count the number

of squares inside the figure, estimating half squares. Use a for a whole square and a for a half square. There are approximately 24 whole squares and 14 half squares, so the area is about Holt Geometry 9-3 Composite Figures Example 3: Finding Areas in the Coordinate Plane by Subtracting

Find the area of the polygon with vertices A(4, 1), B(2, 4), C(4, 1), and D(2, 2). Draw the polygon and close it in a rectangle. Area of rectangle: A = bh = 8(6)= 48 units2. Holt Geometry 9-3 Composite Figures Example 3 Continued Area of triangles:

The area of the polygon is 48 9 3 9 3 = 24 units2. 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 cm2 50 ft2 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 cm2 Holt Geometry