The sum of the angles of a triangle is two right angles. This postulate is equivalent to the parallel postulate.
Triangle Postulate
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References
Dunham, W. Journey through Genius: The Great Theorems of Mathematics. New York: Wiley, p. 54, 1990.Referenced on Wolfram|Alpha
Triangle PostulateCite this as:
Weisstein, Eric W. "Triangle Postulate." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/TrianglePostulate.html