Angles are measured in degrees (°). A full turn is 360°, a half turn is 180° and a quarter turn is a right angle, 90°.
An acute angle is less than 90°. An obtuse angle is between 90° and 180°. A straight angle is exactly 180°, a straight line. A protractor measures angles: line its center up with the corner and its zero line along one arm, then read where the other arm crosses the scale.
Worked example
An angle measures 75°. What type of angle is it?
- Compare with 90°.
- 75° is less than 90°.
Answer:acute
Key words
- degree (°)
- the unit for measuring angles
- protractor
- a tool for measuring angles
- vertex
- the point where the two arms of an angle meet
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Common Core-referenced: 4.G.A.1, 4.MD.C.5