Definition: 1.08: Plane Angle

And a plane angle is the inclination of the lines to one another, when two lines in a plane meet one another and are not lying in a straight line. .

Modern Definition

When two lines meet in a plane in a point, then we say that the lines build a plane angle.

Definitions: 1
Propositions: 2 3

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Adapted from (subject to copyright, with kind permission)

  1. Fitzpatrick, Richard: Euclid's "Elements of Geometry"