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Thales's theorem
Angle formed by a point on a circle and the 2 ends of a diameter is a right angle / From Wikipedia, the free encyclopedia
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For the theorem sometimes called Thales' theorem and pertaining to similar triangles, see intercept theorem.
In geometry, Thales's theorem states that if A, B, and C are distinct points on a circle where the line AC is a diameter, the angle ∠ ABC is a right angle. Thales's theorem is a special case of the inscribed angle theorem and is mentioned and proved as part of the 31st proposition in the third book of Euclid's Elements.[1] It is generally attributed to Thales of Miletus, but it is sometimes attributed to Pythagoras.
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