LEARN NC

K–12 teaching and learning · from the UNC School of Education

What's important about triangles?

http://illuminations.nctm.org/LessonDetail.aspx?ID=L235

A lesson plan for Grades 4–5 Mathematics

Provider: National Council of Teachers of Mathematics

About this resource

Appropriate grades
4–5
Subjects
mathematics (geometry)
Provider
National Council of Teachers of Mathematics

Legal

Creative Commons License

This catalog record is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License. This license applies to the content of this page only and does not apply to the referenced website.

Students explore the importance of the side lengths of a triangle and when triangles can or cannot be constructed on the basis of these lengths. Illuminations provides an activity sheet and detailed instructions for completing the lesson.

Students will:

  • Discover that it is not possible to construct some triangles from given lengths.
  • Discover a rule that states whether or not it is possible to construct triangles from given lengths.
  • Learn about the perimeter of a triangle.

NCTM Standards and Expectations:

  • Make and test conjectures about geometric properties and relationships and develop logical arguments to justify conclusions.
  • Build and draw geometric objects.
  • Develop strategies for estimating the perimeters, areas, and volumes of irregular shapes.

North Carolina Curriculum Alignment

Mathematics (2004)

Grade 4

  • Goal 2: Measurement - The learner will understand and use perimeter and area.
    • Objective 2.01: Develop strategies to determine the area of rectangles and the perimeter of plane figures.
    • Objective 2.02: Solve problems involving perimeter of plane figures and areas of rectangles.
  • Goal 3: Geometry - The learner will recognize and use geometric properties and relationships.
    • Objective 3.01: Use the coordinate system to describe the location and relative position of points and draw figures in the first quadrant.
    • Objective 3.02: Describe the relative position of lines using concepts of parallelism and perpendicularity.
    • Objective 3.03: Identify, predict, and describe the results of transformations of plane figures.
      • Reflections.
      • Translations.
      • Rotations.

Grade 5

  • Goal 2: Measurement - The learner will recognize and use standard units of metric and customary measurement.
    • Objective 2.02: Identify, estimate, and measure the angles of plane figures using appropriate tools.
  • Goal 3: Geometry - The learner will understand and use properties and relationships of plane figures.
    • Objective 3.01: Identify, define, describe, and accurately represent triangles, quadrilaterals, and other polygons.
    • Objective 3.02: Make and test conjectures about polygons involving:
      • Sum of the measures of interior angles.
      • Lengths of sides and diagonals.
      • Parallelism and perpendicularity of sides and diagonals.