Instructional Activity# Calculate the Slope

Lesson 7. Unit 3. Grade 8 Open Up Resources

Open Up Resources10 min(s)

This Instructional Activity is a part of the Lesson 7, Unit 3, Grade 8. The purpose of this task is to develop a quick method or formula to calculate the slope of a line based on the coordinates of two points. It is not critical or even recommended to use the traditional formula invoking subscripts. The goal is for students to realize that they can calculate the vertical and horizontal side lengths of the slope triangle without a grid (eventually without even drawing the slope triangle) and that the slope is the quotient of these side lengths. After students compute the slopes of three specific lines they generalize the procedure. Students are asked to express regularity in repeated reasoning to both describe a procedure in words and then as an algebraic expression.