Réponse :
bonjour
identité remarquable : a² - b² = (a+b)(a-b)
a. (5x + 3)² = 16
(5x + 3)² - 16 = 0
(5x + 3)² - 4² = 0
( 5x + 3 + 4 ) ( 5x + 3 - 4 ) = 0
(5x + 7) ( 5x - 1 ) = 0
5x + 7 = 0 ou 5x - 1 = 0
x =-7/5 ou x = 1/5
b. 49 = (8x – 3)²
(8x - 3)² - 49 = 0
(8x - 3) ² -7² = 0
(8x - 3 - 7 )( 8x - 3 + 7 ) = 0
(8x - 10) ( 8x + 4) = 0
8x -10 = 0 ou (8x + 4 ) = 0
x = 10/8 ou x = -4/8
x = 5/4 ou x =-1/2
voila :)
