Réponse :
bonsoir
a + b = 11
a - b = 4
a = 11 - b
11 - b - b = 4
- 2 b = 4 - 11
- 2 b = - 7
b = 3.5
a + 3.5 = 11
a = 11 - 3.5
a = 7.5
a = 7.5 et b = 3.5
a + b = 7.5 + 3.5 = 11
a - b = 7 .5 - 3.5 = 4
a² = 7.5 ² = 56.25
b ² = 3.5 ² = 12.25
a² - b² = 56 .25 - 12.25 = 44
faire a² - b² , c'est poser l'identité remarquable
a² - b² = ( a + b ) ( a - b )
a² - b² = a² - ab + ba - b² = a² - b²
exemples
a = 5 et b = 2
( a - b) ( a + b) = a² - b²
( 5 - 2 ) ( 5 + 2 ) = 25 - 4 = 21
