Lesson plan

# 3. Use scale factors to create similar shapes (A)

teaches Common Core State Standards CCSS.Math.Content.8.G.A.3 http://corestandards.org/Math/Content/8/G/A/3
teaches Common Core State Standards CCSS.Math.Practice.MP6 http://corestandards.org/Math/Practice/MP6

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Lesson objective: Apply understanding that a dilation of a two-dimensional shape produces a shape that is smaller than, larger than, or the same size as the original shape by drawing a diagram of a farm.

Students bring prior knowledge of proportionality from 7.RP.A.2. This prior knowledge is extended to dilations as students determine the impact when applying a scale factor given the areas of buildings and crops on the farm. A conceptual challenge students may encounter is applying a consistent scale factor in determining the scale and drawing the rectangles.

The concept is developed through work with coordinate planes/grids, which allow students to identify the coordinates of the preimage then apply the scale factor to the coordinates.

This work helps students deepen their understanding of equivalence because corresponding angles are congruent while the scale factor describes the relationship of the side lengths.

Students engage in Mathematical Practice 6 (attend to precision) as they identify the dimensions of the images given the area of the different crops and buildings.

Key vocabulary:

• dilation
• enlargement
• reduction
• scale factor

Special materials needed:

• graph paper
• highlighters or colored pencils to assist students in identifying the various images