Perimeters and areas of composite figures A composite

Perimeters and areas of composite figures A composite figure is a plane figure made up of simple shapes or a 3 -dimensional figure made up of simple 3 -dimensional figures.

Perimeter • The perimeter of a plane composite figure is the sum of the lengths of its sides 20 in. 12 in.

Be careful !!! • Can the perimeter of a composite figure be found by adding the perimeters of the shapes that compose it? • NO! NO! because this would be counting the "internal sides" and they should not be counted at all.

Area congruence postulate Postulate 19 • If 2 polygons are congruent, then they have the same area

Area addition postulate Postulate 20 • The area of a region is equal to the sum of the areas of its nonoverlapping parts • A = A 1 + A 2 + A 3 A 1 A 2

HINT • Sometimes a figure will need to be divided into parts in order to find the area. Look for parts of the figure that appear to be rectangles or triangles and draw dotted lines to indicate how the figure should be divided

• The Area Congruence postulate and the Area Addition postulate make it possible to find the area of complex composite figures by breaking them down into simpler shapes and finding the area of each shape

Find Area and perimeter 7 ft 6 ft 5 ft 3 ft 4 ft

Areas of composite figures by subtracting • Find the area of the shaded region 10 in.