Topics
10. Shapes and angles
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Australia
Year 5

10.05 Estimate angles

Lesson
Practice

Are you ready?

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

Examples

Example 1

Which of these angles is larger?

A
Image of a right angle.
B
Image of an obtuse angle
Worked Solution
Create a strategy

Choose the option with a larger turn between the lines.

Apply the idea

The answer is option B.

Idea summary

Angles can be compared by how large the turn is between the lines.

Estimate angles

Let's see how we can use angles we know to estimate other angles.

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Examples

Example 2

Which angle is equal to 45 degrees?

A
This image shows an angle bigger than a right angle. Ask your teacher for more information.
B
This image shows a very small angle. Ask your teacher for more information.
C
This image shows an angle that is about half a right angle. Ask your teacher for more information.
Worked Solution
Create a strategy

Recall that a 45\degree angle is half of a 90\degree angle, or right angle:

A right angle
Apply the idea

Option A is larger than a right angle. Option B looks smaller than half a right angle. Option C looks like half a right angle.

So the answer is option C.

Idea summary

If we remember some important angles, we can use those to estimate other angles.

Outcomes

AC9M5M04

estimate, construct and measure angles in degrees, using appropriate tools including a protractor, and relate these measures to angle names

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