Perimeters and areas of composite figures

1
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.

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Perimeter

• The perimeter of a plane composite figure is the
  sum of the lengths of its sides

20 in.
12 in.
3
Be careful !!!

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

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Area congruence postulatePostulate 19

• If 2 polygons are congruent, then they have the
  same area

5
Area addition postulatePostulate 20

• The area of a region is equal to the sum of the
  areas of its nonoverlapping parts
• A A1 A2 A3

A3
A2
A1
6
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

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• 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

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Find Area and perimeter
7 ft
3 ft
6 ft
4 ft
5 ft
9
Areas of composite figures by subtracting

• Find the area of the shaded region

10 in.
10 in.