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12. Geometry
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Stage 3

12.10 Angles and angle types

Lesson
Practice
Lesson

Are you ready?

Being able to  identify an angle  can help us in this lesson. Let's try this problem to review.

Examples

Example 1

Which of the following is a right angle?

A
A right angle
B
An acute angle.
Worked Solution
Create a strategy

Look for the angle with a small square in the corner.

Apply the idea

Option A has a small square at the corner, so the answer is option A.

Idea summary

A right angle is exactly 90\degree.

Types of angles

This video explains about acute, right, obtuse, straight, and reflex angles, as well as revolutions.

Loading video...

Examples

Example 2

Select the obtuse angle:

A
A straight angle
B
A right angle
C
An obtuse angle
D
An acute angle
Worked Solution
Create a strategy

Use this image to help you:

A circle with markings at 0, 90 degrees and 180 degrees. Ask your teacher for more information.

Rotate each angle so that one arm lies over the start.

Apply the idea

The answer is Option C.

An obtuse angle
Idea summary

A full revolution is made up of 360 degrees, a single degree is written 1\degree.

Angle typeAngle size
\text{Acute angle}\text{Larger than } 0 \degree, \text{smaller than } 90\degree.
\text{Right angle}90\degree
\text{Obtuse angle}\text{Larger than } 90\degree, \text{smaller than } 180\degree.
\text{Straight angle}180\degree
\text{Reflex angle}\text{Larger than } 180\degree, \text{smaller than } 360\degree.
\text{Full revolution}360\degree

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