# Angles in a straight line and around a point

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Angles in a straight line and around a point

Lesson Objectives To understand the sum of angles in a straight line
To understand the sum of angles around a point To be able to answer questions by using these two rule to find unknown angles.

What angle is this? =90° A right-angle

If there are 90° in a right-angle, how many are their in a straight line?
90°+90°= 180°

As there are 180° in a straight line, what is the unknown angle here?
135° 45° 180°- 45° = 135°

If the angles in a straight line equal 180°, what do the angles around a point add up to?
90° 90° 90° 90° 90°+90°+90°+90°= 360°

As there are 360° around a point, what is the unknown angle here?
45° 45° 100° ? 110° 360° - 45° - 60° - 45° - 100° = 110°

Copy out the following definitions:
45° ? 180°- 45° = 135° Angles in a straight line = 180° 45° 60° 100° ? 360° - 45° - 60° - 45° - 100° = 110° Angles around a point = 360°

Plenary What are the missing angles?
57° 123° a 89° b 46° 45°

What are the missing angles?
150° 30° X Z 30° Y 150°

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