Construction du projeté orthogonal

Les outils

Le prolongement

Le prolongement est assuré par l'axiome segment_construction

segment_construction : ∀ A B C D : Point, ∃ E : Point, Bet A B E /\ B E ≡ C D

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Le milieu sous condition

Le théorème l7_25 assure l'existence du mileu de deux points équidistants d'un troisième point

l7_25 : ∀ A B C, CA ≡ CB → ∃ X, X milieu de A B

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La construction

Dans le cadre de la démonstration du théorème l8_18_existence :

l8_18_existence : ∀ A B C, ¬Col A B C → ∃ X, Col A B X /\ Perp A B C X

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il est nécéssaire de construire le point X en utilisant exclusivement le prolongement et le milieu sous condition présentés plus haut

Etape 0

Hypothèse : ¬ Col A B C

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suivant

Etape 1

on prolonge BA par Y de sorte que AY ≡ AC

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suivant

Etape 2

puisque par construction AY ≡ AC on peut construire le milieu P de C Y

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suivant

Etape 3

On prolonge AY par Z de sorte que AY ≡ PY

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suivant

Etape 4

On prolonge CY par Q de sorte que YQ ≡ AY

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suivant

Etape 5

On prolonge QZ par Q' de sorte que ZQ' ≡ QZ

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suivant

Etape 6

On prolonge QY par C' de sorte que YC' ≡ YC

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suivant

Etape 7

puisque par construction YC ≡ YC' on peut construire le milieu X de C C'

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Il reste a prouver que X est bien le projeté orthogonal de C sur A B (500 pas de démonstration)

retour à l'acceuil Gabriel Braun - octobre 2011 statistiques