Lesson plan

4. Find area by creating a new region of known area (C)

teaches Common Core State Standards CCSS.Math.Content.6.G.A.1 http://corestandards.org/Math/Content/6/G/A/1
teaches Common Core State Standards CCSS.Math.Practice.MP4 http://corestandards.org/Math/Practice/MP4
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Lesson objective: Understand that it is possible to find the area of a figure by creating a new region of known or equal area.

Students bring prior knowledge of finding the area of a rectangle from 4.MD.A.3, G04_U02. This prior knowledge is extended to figures where it is necessary to cut off a piece and move it to create a known figure as students continue to decompose and lay the groundwork for developing area formulas for other figures. A conceptual challenge students may encounter is visualizing how to break apart a figure or understanding how to subtract sections to find the area.

The concept is developed through work with drawings and the use of graph paper, which allows students to better visualize the parts of the figures.

This work helps students deepen their understanding of equivalence because students are able to see the new figure they create is equivalent in area to the original figure.

Students engage in Mathematical Practice 4 (Model with mathematics) as they view, manipulate, and create models to represent decomposing the figures.

Key vocabulary:

  • area
  • decompose
  • triangle

Special materials needed:

  • Graph paper may be helpful to some students.