13.3 Calculating angles_1allr

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Which angle's size is
between 90° and 180°?

Types of angles

Acute angle: between 0° and 90°
Right angle: 90°
Obtuse angle: between 90° and 180°
Straight angle: 180°
Reflex angle: between 180° and 360°
Full angle: 360°
(A full angle is also called a full turn)

Both a straight angle and a full turn look like a straight line. The arc is used to show it is an angle.

Calculating angles

Opposite angles

Opposite angles are the angles on opposite sides of the point of intersection of two lines. Opposite angles are always equal.

Calculating angles

What type of angle is            ?

∠A​4​​

What type of angle is angle A4?

1. Acute angle
2. Right angle
3. Obtuse angle
4. Straight angle

Calculating angles

Which angle is the opposite
angle of             ?

∠A​1​​

Which angle is the opposite of angle A1?

1. ∠A​2​​
2. ∠A​3​​
3. ∠A​4​​
4. ∠A​5​​

Calculating angles

What size is             ?

∠A​2​​

How many degrees
is angle A2?

Calculating angles

(because they are opposite angles)


(because it is a right angle)

∠A​3​​=∠A​1​​=57°

∠A​4​​=90°

Calculating angles

                        and            are together
a ......

∠A​1​​,∠A​5​​

∠A​4​​

Angle A1, angle A5 and
Angle A4 are together a ....

1. full turn
2. reflex angle
3. straight angle
4. right angle

Calculating angles

∠A​5​​=180−90−57=33°

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