This Instructional Activity is a part of the Lesson 26, Unit 4, Grade 8. What did you notice about each of the systems you graphed in Exercises 1-3? For each exercise, the graphs of the given linear equations look like parallel lines. What did you notice about the slopes in each system? Provide time for students to write their conclusions. Share the theorem with them, and have students compare the conclusions that they reached to the statements in the theorem.