I = (7x - 3)² - 25 a) Factoriser I b) Résoudre l'équation I = 0

Bonsoir,

I = (7x - 3)² - 25

a) Factoriser I

I = (7x - 3) - 5²
 = [(7x - 3) + 5] [(7x - 3) - 5]
 = (7x - 3 + 5)(7x - 3 - 5)
 = (7x + 2)(7x - 8)

b) Résoudre l'équation I = 0

(7x + 2)(7x - 8) = 0
7x + 2 = 0   ou  7x - 8 = 0
7x = -2    ou   7x = 8
x = -2/7    ou   x = 8/7

S = {-2/7 ; 8/7}