During this lesson, you will:  Estimate the area of irregular shapes  Decompose irregular polygons into squares, rectangles, triangles, and other familiar shapes  Determine the area of an irregular polygon by summing the areas of its composite shapes

Area = ___________________________ Area = __________________________ Area (rect./square) = __________________ Area = __________________________ ½ bh* bh* bh ½ h* (b 1 + b 2 ) Л r 2

KEY to Irregular Figure Areas To find the area of an irregular figure:  Divide the figure into familiar geometric figures.  Use known measures (and parallel sides) to determine unknown measures.  Find the area of each familiar shape.  ADD the sum of the areas of each shape to find the total area. Method: Divide and Conquer

A.Divide each figure below 2 different ways. B. Find missing dimensions. C. Find each area. D. Find total area. 20 cm 5 cm 4cm 5 cm 4cm 20 cm 2 40 cm 2 60 cm 2 80 cm 2 60 cm 2 40 cm 2 20 cm cm 2

Find the area of the figure to the nearest tenth, if necessary. 4 cm 12 cm + = A = ½ bh A = bh 60 cm 2

KEY to Irregular Figure Areas Find the area of each shaded region. Method: Area (larger) – Area (smaller) 28 cm 15 cm 5 cm 10 cm A = bh 370 cm 2

KEY to Irregular Figure Areas Method: Area (larger) – Area (smaller) 3 cm 6 cm 11 cm 3 cm 6 cm 3 cm A = bh - 51 cm 2

KEY to Irregular Figure Areas Method: Area (larger) – Area (smaller) Find the area of the shaded region. R = 12 cm; r =8 cm A = πr 2 Answer: 80 πcm 2 -

Final Checks for Understanding In your own words, summarize a general technique for finding areas of irregular figures. Absent? Check out this link on irregular areas:

Final Checks for Understanding Find the area of the shaded region. 120 cm cm cm 2

Homework Assignment Area: Irregular Figures WS, plus textbook: