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Class 5
Chapter 3: Angles as Turns
An angle is the amount of turn between two rays. A quarter turn is 90° (a right angle), a half turn is 180°, and a full turn is 360°. Angles smaller than 90° are acute; between 90° and 180° they are obtuse.
Learning outcomes
- Describe turns as quarter, half and full
- Identify right, acute and obtuse angles
Activities
- Turn-the-arrow direction game
Worked examples
Read through these first, then try the practice below.
Example 1 — Right angle
What kind of angle is exactly 90°?
Solution: A right angle.
Example 2 — Acute or obtuse?
Is a 45° angle acute or obtuse?
Solution: Acute — it is less than 90°.
Self-do practice
Question 1 of 3 · Score 0/0How many degrees are there in a full turn?
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