Geometry

Level 1

Angle names

Acute angle

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An acute angle is between 0 and 90 degrees

Angle names

Obtuse angle

An obtuse angle is between 90 and 180 degrees

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Angle names

Reflex angle

A reflex angle is between 180 and 360 degrees

Angle names

Right angle

A right angle is 90 degrees

Angle names

Right angle

A right angle is 90 degrees

Angle names

Straight angle

A straight line is 180 degrees

Naming angles

• The angle is at B

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∠ABCA

B C

Guessing the angle size

• The clock is divided into 12 hours.

• One complete circle is 360 degrees.

• Each hour makes 30 degrees.

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30°

€

60°

€

90°

€

120°

€

210°

€

270°

€

180°

What angle do the hands of the clock make?

• 4 lots of 30 degrees.• 120 degrees.• OR the reflex angle

is 240 degrees.

Guess the angle size

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60°

€

90°

€

150°

€

170°OR

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300°

€

210°

€

270°

€

190°

Complementary angles

• Two angles which add up to 90 degrees are said to be complementary.

Complementary angles

• What is the complement of 58 degrees?

?

Complementary angles

• 32 degrees

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58+ 32 =90

Complementary angles

• What is the complement of 45 degrees?

?

?

Complementary angles

• 45 degrees

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45+ 45=90

Supplementary angles

• Two angles which add up to 180 degrees are said to be supplementary.

Supplementary angles

• What is the supplement of 120 degrees?

?

?

Supplementary angles

• 60 degrees?

?

Supplementary angles

• What is the supplement of 40 degrees?

?

Supplementary angles

• What is the supplement of 140 degrees?

Measuring angles

• We use a protractor to measure angles.

There are two scales marked on your protractor

First decide if your angle is acute or obtuse

This angle is acute

Read the acute scale.

The angle is 56 degrees.

This angle is obtuse.

Read the obtuse scale.

The angle is 124 degrees.