Angle Sums

This chapter explores Angle sums. It covers; angles on a line total 180°, angles around a point total 360° and angles in a triangle total 180°.

Special angles

You’ll need to know the following facts while adding angles.
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Degrees in a half-turn

You must understand that two right angles make a straight line.
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Two 90° make 180°. Any angles that fit together to make a straight line add up to 180°.

Finding a missing angle on a line

The following straight line is made up of 3 angles.
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All angles add up to 180°.

Angles in a triangle

This section explores angles in a triangle. Take a triangular piece of paper as shown below.
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Suppose you coloured in the 3 angles at the edges as shown below.
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Then rip off the 3 angles and move them to a straight line.
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You’ll notice that the three angles fit on a straight line and they add up to 180°.