# Sum of External Angles of Polygon equals Four Right Angles

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## Theorem

Let the external angles of a polygon be generated in the same direction going around the polygon.

Then the sum of all these external angles equals $4$ right angles.

## Proof

## Sources

- 1968: M.N. Aref and William Wernick:
*Problems & Solutions in Euclidean Geometry*... (previous) ... (next): Chapter $1$: Triangles and Polygons: Theorems and Corollaries $1.9$ - 2014: Christopher Clapham and James Nicholson:
*The Concise Oxford Dictionary of Mathematics*(5th ed.) ... (previous) ... (next): Entry:**polygon**