Big Ideas:
Trapezoids can be decomposed into rectangles and triangles.
The area of a trapezoid can be solved for by finding the areas of the rectangles and triangles within the shape.
This lesson builds on students’ work with decomposing polygons into triangles, rectangles, and other shapes. In this task, students will decompose trapezoids into rectangles and triangles to find their areas. By decomposing trapezoids into rectangles and triangles, students will continue to build on their understanding of the concept that area is additive. The mathematical concepts in this lesson build toward students’ future work with finding the areas of 2-D composite figures, surface area, and the slicing of 3-D figures in grades 6-8.
Vocabulary: trapezoid, rectangle, triangle, area, additive, decompose
Special Materials:
Grid Paper
Lesson plan