An angle is a turn between two lines that meet. A right angle is a quarter turn, like the corner of a book. It measures 90 degrees, written 90°.
An angle smaller than a right angle is acute. An angle bigger than a right angle but smaller than a straight line is obtuse. A straight line makes a half turn, which is 180°. Compare an angle with the corner of a page to decide its type.
Worked example
An angle measures 130°. What type of angle is it?
- 130° is more than 90°.
- It is less than 180°, so it is not a straight line.
Answer:obtuse
Key words
- right angle
- a quarter turn, 90°
- acute
- smaller than a right angle
- obtuse
- between a right angle and a straight line
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