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Lesson Plan

10. Find unknown measures in triangles (A)

teaches Common Core State Standards CCSS.Math.Content.7.G.A.2 http://corestandards.org/Math/Content/7/G/A/2
teaches Common Core State Standards CCSS.Math.Content.7.G.B.5 http://corestandards.org/Math/Content/7/G/B/5
teaches Common Core State Standards CCSS.Math.Practice.MP3 http://corestandards.org/Math/Practice/MP3
teaches Common Core State Standards CCSS.Math.Practice.MP5 http://corestandards.org/Math/Practice/MP5
teaches Common Core State Standards CCSS.Math.Practice.MP7 http://corestandards.org/Math/Practice/MP7
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Lesson objective: Apply their understanding of the Triangle Inequality Theorem to determine an efficient design for a kitchen.

This lesson provides an opportunity for students to apply their knowledge and understanding the the sum of any two lengths of a triangle must be greater than the length of the third side to a real-life situation. Students are asked to consider three possible locations for a stove in a kitchen so that an efficient "kitchen work triangle" can be formed.

Key Concept students will use: 

  • The sum of the lengths of two sides of a triangle must be greater than the length of the third side, and this can be informally proven.

Skills students will use:

  • the Triangle Inequality Theorem to decide an unknown measure, the distance from the sink to the stove in a kitchen.
  • when given two sides of a triangle, students will determine the range of acceptable values for the length of the third side of the triangle.

Students engage in Mathematical Practice #3 (construct viable arguments and critique the reasoning of others) as they decide the best location for a stove that will produce the most efficient design for a kitchen.​

Key vocabulary: 

  • acute triangle
  • angle
  • base angle
  • isosceles triangle
  • obtuse triangle
  • right triangle
  • side
  • triangle angle sum
  • Triangle Inequality Theorem

Special materials needed:

  • protractor
  • ruler
Related content

Appears in

Geometric constructions

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