ACT Preparation / Unit 13 ACT 1208 short lesson, about 20 seconds
The Exterior Angle
Captions available
The idea
An exterior angle of a triangle, formed by extending one side, equals the sum of the two interior angles not next to it.
In practice
Interior angles of 40° and 75° give an exterior angle of 115° at the third vertex.
Where people slip
The exterior angle and its neighboring interior angle are supplementary: 115° and 65°.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
Builds on
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