Angles extérieurs d'un polygone

On a marqué les angles extérieurs d'un triangle.
Quelle est la somme de ces trois angles ?

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Quelle est la somme des angles extérieurs d'un quadrilatère convexe ? Sorry, the GeoGebra Applet could not be started. Please make sure that Java 1.4.2 (or later) is installed and active in your browser (Click here to install Java now)

Même question pour un pentagone. Sorry, the GeoGebra Applet could not be started. Please make sure that Java 1.4.2 (or later) is installed and active in your browser (Click here to install Java now)

Voici un polygone régulier de 12 côtés. Que valent ses angles ? Sorry, the GeoGebra Applet could not be started. Please make sure that Java 1.4.2 (or later) is installed and active in your browser (Click here to install Java now)