Idea 6of 24Builds onBenchmark angles for estimating
Acute, right, obtuse or straight
What names do angles get from their size?
Today you'll discover
- the angle you compare every angle with
- the four names for angles
- how to name an angle from its degrees
Think firstCompare it with a square corner
Compared with a square corner, 90°, is this angle wider or narrower?
Decide first, then press Next. Compare the arm with the upright 90° line.
An angle of 110° opening from a flat arm. Two shaded zones then split the half circle: up to 90° marked acute and from 90° to 180° marked obtuse. Then a square corner marked with a small square and named right, a flat line named straight, and the 110° angle named obtuse. The last step shows a narrow angle of 35°.
See the whole ideathe big idea and the key word, in one place
The big idea
Acute is under 90°, right is exactly 90°, obtuse is between 90° and 180°, straight is 180°.
Compare themAcute: less than 90°. Right: exactly 90°, a square corner. Obtuse: more than 90° but less than 180°. Straight: exactly 180°, a flat line.
Easy to get wrongA right angle does not have to point up and to the right. Turned any way, a square corner is still a right angle.
Key words
- acute angle
- an angle less than 90°
- right angle
- an angle of exactly 90°, a square corner
- obtuse angle
- an angle more than 90° and less than 180°
- straight angle
- an angle of exactly 180°: its arms make a straight line
Ready to use it?
- Name an angle as acute, right, obtuse or straight.