Common Core State Standards indicate that learners should be able to "Find areas of rectilinear figures by decomposing them into non-overlapping triangles." The learners work on this standard in this video segment.
These resources are part of KET's Math Instructional Strategies: Geometry collection.
Teacher Interview: Comparison of Inquiry and Lecture-Based Lessons, Part 1 (Video)
Teacher Interview: Comparison of Inquiry and Lecture-Based Lessons, Part 2 (Video)
Being able to apply knowledge in different mathematical solving situations is a sign of depth of understanding. Sometimes learners need to work a problem both "forward" and "backward" to truly understand the concept.