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3e année secondaire

Cours : 3e année secondaire > Chapitre 11 

Leçon 2: Pythagore : Application au calcul de distances
Mathématiques
3e année secondaire
Géométrie : Pythagore, triangle rectangle et trigonométrie
Pythagore : Application au calcul de distances
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Distance entre deux points

Google Classroom
Suivant les pays les notations sont différentes. Nous utilisons AB pour désigner la longueur du segment [AB]. Peut-être utilisez-vous |AB|.
Quels que soient A, left parenthesis, start color #1fab54, x, start subscript, 1, end subscript, end color #1fab54, comma, start color #e07d10, y, start subscript, 1, end subscript, end color #e07d10, right parenthesis et B, left parenthesis, start color #1fab54, x, start subscript, 2, end subscript, end color #1fab54, comma, start color #e07d10, y, start subscript, 2, end subscript, end color #e07d10, right parenthesis la start color #11accd, start text, d, i, s, t, a, n, c, e, end text, end color #11accd entre A et B, c'est-à-dire la longueur du segment open bracket, A, B, close bracket est :
A, B, equals, square root of, left parenthesis, start color #1fab54, x, start subscript, 2, end subscript, minus, x, start subscript, 1, end subscript, end color #1fab54, right parenthesis, squared, plus, start color #e07d10, left parenthesis, y, start subscript, 2, end subscript, minus, y, start subscript, 1, end subscript, end color #e07d10, right parenthesis, squared, end square root
D'où vient cette formule et comment l'appliquer ?

Comprendre la formule

On place les points de coordonnées left parenthesis, start color #1fab54, x, start subscript, 1, end subscript, end color #1fab54, space, ;, start color #e07d10, y, start subscript, 1, end subscript, end color #e07d10, right parenthesis et left parenthesis, start color #1fab54, x, start subscript, 2, end subscript, end color #1fab54, space, ;, start color #e07d10, y, start subscript, 2, end subscript, end color #e07d10, right parenthesis.
The first quadrant of a coordinate plane with two tick marks on the x axis labeled x one and x two. There are two tick marks on the y axis labeled y one and y two. There is a point at x one, y one and another point at x two, y two.
Il s'agit de calculer la start color #11accd, start text, d, i, s, t, a, n, c, e, end text, end color #11accd entre ces deux points, c'es-à-dire la longueur du segment tracé en bleu.
The first quadrant of a coordinate plane with two tick marks on the x axis labeled x one and x two. There are two tick marks on the y axis labeled y one and y two. There is a point at x one, y one and another point at x two, y two. A line connects the two points.
Pour calculer cette start color #11accd, start text, l, o, n, g, u, e, u, r, end text, end color #11accd, on trace un triangle rectangle ce qui permettra d'utiliser le théorème de Pythagore.
The first quadrant of a coordinate plane with two tick marks on the x axis labeled x one and x two. There are two tick marks on the y axis labeled y one and y two. There is a point at x one, y one and another point at x two, y two. A line connects the two points. A third unlabeled point is at x two, y one with a line connecting from it to the point at x two, y two and another line connecting from it to the point at x one, y one forming a right triangle.
La longueur du côté de l'angle droit tracée en vert est start color #1fab54, x, start subscript, 2, end subscript, minus, x, start subscript, 1, end subscript, end color #1fab54:
The first quadrant of a coordinate plane with two tick marks on the x axis labeled x one and x two. There are two tick marks on the y axis labeled y one and y two. There is a point at x one, y one and another point at x two, y two. A line connects the two points. A third unlabeled point is at x two, y one with a line connecting from it to the point at x two, y two and another line connecting from it to the point at x one, y one forming a right triangle. The hypotenuse of the right triangle is unknown and the side made from the point at x one, y one and x two, y one is labeled x two minus x one.
De même, la longueur de l'autre côté de l'angle droit est start color #e07d10, y, start subscript, 2, end subscript, minus, y, start subscript, 1, end subscript, end color #e07d10 :
The first quadrant of a coordinate plane with two tick marks on the x axis labeled x one and x two. There are two tick marks on the y axis labeled y one and y two. There is a point at x one, y one and another point at x two, y two. A line connects the two points. A third unlabeled point is at x two, y one with a line connecting from it to the point at x two, y two and another line connecting from it to the point at x one, y one forming a right triangle. The hypotenuse of the right triangle is unknown and the side made from the point at x one, y one and x two, y one is labeled x two minus x one. The third side is labeled y two minus y one.
On utilise le théorème de Pythagore :
start color #11accd, question mark, end color #11accd, squared, equals, left parenthesis, start color #1fab54, x, start subscript, 2, end subscript, minus, x, start subscript, 1, end subscript, end color #1fab54, right parenthesis, squared, plus, start color #e07d10, left parenthesis, y, start subscript, 2, end subscript, minus, y, start subscript, 1, end subscript, end color #e07d10, right parenthesis, squared
La start color #11accd, start text, d, i, s, t, a, n, c, e, end text, end color #11accd cherchée est :
start color #11accd, question mark, end color #11accd, equals, square root of, left parenthesis, start color #1fab54, x, start subscript, 2, end subscript, minus, x, start subscript, 1, end subscript, end color #1fab54, right parenthesis, squared, plus, start color #e07d10, left parenthesis, y, start subscript, 2, end subscript, minus, y, start subscript, 1, end subscript, end color #e07d10, right parenthesis, squared, end square root
On obtient la formule de la distance entre deux points de coordonnées données.
Si vous n'arrivez pas à mémoriser cette formule, il est toujours possible de tracer un triangle rectangle dont l'hypoténuse est le segment en question et d'appliquer le théorème de Pythagore.

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