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gcse maths by metcalf and bowles
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Edexcel GCSE Modular Maths #1(Higher) by by Karen Hughes, published by Heinemann
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GeoGebra : external angle of a triangle

 

 

 

 

The external angle of a triangle equals the sum of the two internal opposite angles.
ACD = ABC + BAC

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The external angle and the internal angle are supplementary.
That is, they add up to 180 deg.
ACB + ACD = 180 deg. (sum of angles in a straight line)

Alginon, Created with GeoGebra

 

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