Consider how extending sides creates supplementary angles that reveal why triangle angles always add up to 180°.
Why the Angles of a Triangle Sum to 180°: A Simple Proof
Browsing Tag
Geometric Proofs
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Proof: Sum of Interior Angles in an N-Sided Polygon
Meta description: “Many geometric proofs reveal why the interior angles of an n-sided polygon sum to a specific value—discover the elegant reasoning behind this fundamental concept.
