geometry · Year 4 · AC9M4M04
Types of angle
An angle is the amount of turn between two arms. Compare it with a right angle (a square corner, 90°) and a straight line (180°). Smaller than a right angle is acute. Exactly a square corner is a right angle. Between a right angle and a straight line is obtuse. A straight line is a straight angle. More than a straight line is reflex: the arc goes the long way round. Arm length never changes the type, and neither does turning the picture.
Sample questions
What type of angle is marked? Choose from: acute, right, obtuse, straight or reflex.
- Compare the marked angle with a right angle, which is a square corner.
- It is smaller than a right angle.
- So it is an acute angle.
Answer: acute
What type of angle is marked? Choose from: acute, right, obtuse, straight or reflex.
- The small square marks a square corner.
- It is exactly a right angle.
- So it is a right angle.
Answer: right
What type of angle is marked? Choose from: acute, right, obtuse, straight or reflex.
- Compare the marked angle with a right angle and with a straight line.
- It is bigger than a right angle but smaller than a straight line.
- So it is an obtuse angle.
Answer: obtuse