11.01 Angles and angle types
Lesson
Are you ready?
Being able to identify the size of angle can help us in this lesson. Let's try this problem to review.
An angle of $90^\circ$90° is shown in the circle below.
What fraction of a full circle is this angle?
$\frac{1}{3}$13
A$\frac{1}{4}$14
B$\frac{1}{6}$16
C$\frac{1}{8}$18
D
Learn
We can use this visual to remember the names for different angle sizes:
This video explains about acute, right, obtuse, straight, and reflex angles, as well as revolutions.
Apply
Select the obtuse angle:
A
B
C
D
Remember!
A full revolution is made up of $360$360 degrees, and a single degree is written as $1^\circ$1°.
| Angle type | Angle size |
|---|---|
| Acute angle | Larger than $0^\circ$0°, smaller than $90^\circ$90°. |
| Right angle | $90^\circ$90° |
| Obtuse angle | Larger than $90^\circ$90°, smaller than $180^\circ$180°. |
| Straight angle | $180^\circ$180° |
| Reflex angle | Larger than $180^\circ$180°, smaller than $360^\circ$360°. |
| Full revolution | $360^\circ$360° |