IM 6.6.6 Lesson: Write Expressions Where Letters Stand for Numbers

① This GeoGebra example is an interactive lesson from the IM 6.6.6 curriculum, demonstrating how to write algebraic expressions where letters represent numbers, and how to interpret these expressions in real contexts. ② Core mathematical concepts include algebraic expressions, variables, constants, and the fundamental idea of using letters to denote unknown or varying quantities, preparing students for equations and functions. ③ Construction highlights: based on the summary, objects A1, A2, B1, C1, D1 are used, likely as points or numeric values, possibly with sliders or input fields to dynamically substitute different numbers into expressions, allowing students to see how the expression's value changes with the variable. ④ Suitable for upper elementary to middle school (grades 6-7), useful for classroom instruction or self-paced exploration, and serves as a teacher resource to bridge concrete arithmetic and abstract algebra.