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  2. Lexell's theorem - Wikipedia

    en.wikipedia.org/wiki/Lexell's_theorem

    Lexell's proof by breaking the triangle A ∗ B ∗ C into three isosceles triangles. The main idea in Lexell's c. 1777 geometric proof – also adopted by Eugène Catalan (1843), Robert Allardice (1883), Jacques Hadamard (1901), Antoine Gob (1922), and Hiroshi Maehara (1999) – is to split the triangle into three isosceles triangles with common apex at the circumcenter and then chase angles ...

  3. Therefore sign - Wikipedia

    en.wikipedia.org/wiki/Therefore_sign

    In logical argument and mathematical proof, the therefore sign, ∴, is generally used before a logical consequence, such as the conclusion of a syllogism. The symbol consists of three dots placed in an upright triangle and is read therefore. While it is not generally used in formal writing, it is used in mathematics and shorthand.

  4. Pons asinorum - Wikipedia

    en.wikipedia.org/wiki/Pons_asinorum

    The pons asinorum in Oliver Byrne's edition of the Elements [1]. In geometry, the theorem that the angles opposite the equal sides of an isosceles triangle are themselves equal is known as the pons asinorum (/ ˈ p ɒ n z ˌ æ s ɪ ˈ n ɔːr ə m / PONZ ass-ih-NOR-əm), Latin for "bridge of asses", or more descriptively as the isosceles triangle theorem.

  5. List of theorems - Wikipedia

    en.wikipedia.org/wiki/List_of_theorems

    The reason given is: ... Lists of theorems and similar statements include: List of algebras; ... Cut-elimination theorem (proof theory) D

  6. Mathematical proof - Wikipedia

    en.wikipedia.org/wiki/Mathematical_proof

    P. Oxy. 29, one of the oldest surviving fragments of Euclid's Elements, a textbook used for millennia to teach proof-writing techniques. The diagram accompanies Book II, Proposition 5. [1] A mathematical proof is a deductive argument for a mathematical statement, showing that the stated assumptions logically guarantee the

  7. Pythagorean theorem - Wikipedia

    en.wikipedia.org/wiki/Pythagorean_theorem

    Proof using similar triangles. This proof is based on the proportionality of the sides of three similar triangles, that is, upon the fact that the ratio of any two corresponding sides of similar triangles is the same regardless of the size of the triangles. Let ABC represent a right triangle, with the right angle located at C, as shown on the ...

  8. Menelaus's theorem - Wikipedia

    en.wikipedia.org/wiki/Menelaus's_theorem

    A proof given by John Wellesley Russell uses Pasch's axiom to consider cases where a line does or does not meet a triangle. [4] First, the sign of the left-hand side will be negative since either all three of the ratios are negative, the case where the line DEF misses the triangle (see diagram), or one is negative and the other two are positive, the case where DEF crosses two sides of the ...

  9. Roberts's triangle theorem - Wikipedia

    en.wikipedia.org/wiki/Roberts's_triangle_theorem

    Branko Grünbaum found the proof in Roberts's original paper "unconvincing", [3] [4] and credits the first correct proof of Roberts's theorem to Robert W. Shannon, in 1979. [1] [5] He presents instead the following more elementary argument, first published in Russian by Alexei Belov.