Geometry
Right Angles – Exactly 90 Degrees
A right angle measures exactly 90° – a quarter of a full turn. It's the angle you see at the corner of a square or rectangle, and it's so fundamental to geometry that it gets its own special diagram symbol: a small square drawn inside the angle's corner, instead of a curved arc.
The name comes from the Latin angulus rectus, meaning “upright angle” – the Romans used the term for the perfectly upright corner formed where a vertical wall meets level, horizontal ground.
Recognising a Right Angle
A right angle measures exactly 90° and is marked in diagrams with a small square symbol, not a curved arc.
How many right angles fit exactly into a straight angle (180°)?
180 ÷ 90 = 2.
Real-Life Application
- Buildings: most walls, doors, and windows are built at right angles for stability.
- Furniture: table and shelf corners are right angles by design.
- Set squares: drafting tools include a fixed 90° corner for precise drawing.
Key Takeaways
- A right angle is exactly 90°, a quarter of a full turn.
- It is marked with a small square symbol, not a curved arc.
- Two right angles together make a straight angle (180°).
Practice: Right Angles
Right Angles