Reflection: Connection to Prior Knowledge Proving Area Formulas for Parallelograms, Triangles and Rhombuses - Section 5: Closure


I really enjoy teaching this lesson because it gives me a chance to give students the experience of how Geometry operates as an axiomatic system. I love how in Geometry we solve problems and then immediately use the solutions to these problems to solve other problems. It really gives me a sense of growth and building. So I like to give students opportunities to experience Geometry in this way as well.

In this lesson we postulate the rectangle area formula. Then we use it to prove the parallelogram area formula, which is in turn used to prove the trapezoid area formula. Not only that, we incorporate things we learned from much earlier in the course like congruent triangles, properties of quadrilaterals, etc. 

Geometry is not a learn and forget kind of subject and this lesson really drives that point home.

  Giving the experience of Geometry as an axiomatic system
  Connection to Prior Knowledge: Giving the experience of Geometry as an axiomatic system
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Proving Area Formulas for Parallelograms, Triangles and Rhombuses

Unit 10: Areas of Plane Figures
Lesson 2 of 8

Objective: SWBAT use composition and decomposition to prove the area formulas for parallelograms, triangles, and rhombuses.

Big Idea: Look deep within...and see a figure whose area formula we've already proven.

  Print Lesson
  75 minutes
triangle formula
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