LEARN NC

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

Discovering the area formula for triangles

http://illuminations.nctm.org/LessonDetail.aspx?ID=L577

A lesson plan for Grades 6–8 Mathematics

Provider: National Council of Teachers of Mathematics

About this resource

Appropriate grades
6–8
Subjects
mathematics (measurement)
Provider
National Council of Teachers of Mathematics

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In this lesson, students develop the area formula for a triangle. Students find the area of rectangles and squares, and compare them to the areas of triangles derived from the original shape. Illuminations provides an activity sheet, an overhead transparency template, a link to an area triangle tool, and detailed instructions for completing the lesson.

Students will:

  • Determine the areas of rectangles and squares.
  • Derive an area formula for triangles.
  • Use the area formula to calculate the area of a triangle or to find one of the dimensions.

NCTM Standards and Expectations:

  • Understand both metric and customary systems of measurement.
  • Understand, select, and use units of appropriate size and type to measure angles, perimeter, area, surface area, and volume.
  • Develop and use formulas to determine the circumference of circles and the area of triangles, parallelograms, trapezoids, and circles and develop strategies to find the area of more-complex shapes.
  • Select and apply techniques and tools to accurately find length, area, volume, and angle measures to appropriate levels of precision.

North Carolina Curriculum Alignment

Mathematics (2004)

Grade 6

  • Goal 2: Measurement - The learner will select and use appropriate tools to measure two- and three-dimensional figures.
    • Objective 2.01: Estimate and measure length, perimeter, area, angles, weight, and mass of two- and three-dimensional figures, using appropriate tools.
    • Objective 2.02: Solve problems involving perimeter/circumference and area of plane figures.

Grade 7

  • Goal 2: Measurement - The learner will understand and use measurement involving two- and three-dimensional figures.
    • Objective 2.01: Draw objects to scale and use scale drawings to solve problems.
    • Objective 2.02: Solve problems involving volume and surface area of cylinders, prisms, and composite shapes.

Grade 8

  • Goal 2: Measurement - The learner will understand and use measurement concepts.
    • Objective 2.01: Determine the effect on perimeter, area or volume when one or more dimensions of two- and three-dimensional figures are changed.
    • Objective 2.02: Apply and use concepts of indirect measurement.