This Fluency Activity is a part of the Lesson 3, Unit 4, Grade 4. In this lesson, students generate a definition of perpendicular lines based on a given figure, use right angles to identify perpendicular lines, identify the symbol for perpendicular lines, and generate their own perpendicular lines with a straight edge. This fluency activity reviews the Concept Developments from Grade 4 Module 3 Lessons 34-38.