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Corollary: Triangulation of Quadrilateral and Sum of Angles

(related to Proposition: 1.32: Sum Of Angles in a Triangle and Exterior Angle)

Since a quadrilateral can be divided into two triangles, the sum of its angles equals four right angles. \[\sum_{i=1}^6 \alpha_i=2\times 180^\circ=4\times 90^\circ\]

Table of Contents

Proofs: 1

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References

Adapted from CC BY-SA 3.0 Sources:

1. Callahan, Daniel: "Euclid’s 'Elements' Redux" 2014

Adapted from (Public Domain)

1. Casey, John: "The First Six Books of the Elements of Euclid"