Perpendicular Lines
Grade 7 Geometry — A Complete Guide
Why Study Perpendicular Lines?
Perpendicular lines are a special case of intersecting lines — they meet at a very specific angle. This fundamental concept in geometry is the basis for many constructions, proofs, and real-world applications. From the corners of your room to the axes on a graph, perpendicular lines are everywhere!
📐 Definition of Perpendicular Lines
Formal Definition: Two lines are perpendicular if they intersect and form a right angle (90°).
- Symbol: The symbol ⊥ means "is perpendicular to"
- If line $a$ is perpendicular to line $b$, we write: $a \perp b$
- In diagrams, a small square at the vertex marks the right angle
🔄 Right Angle Review
- A right angle measures exactly 90°
- It is a quarter of a full rotation (360° ÷ 4 = 90°)
- Always marked with a small square at the vertex
- Perpendicular lines always form right angles
$a \perp b$
🖱️ Interactive: Explore Perpendicular Lines
Drag the points to see how perpendicular lines always form four 90° angles.
Interactive visualization — available in the full lesson