Réponse :
Explications étape par étape :
a )G(x) = 25x2 - 9+ (Sx - 3)(x - 15)
= 25 x^2 - 9 + 5x^2 - 75 x - 3 x + 45
= 30 x^2 - 78 x + 36
b)
25 x^2 -9 = (5x - 3) (5x +3)
Cela vient de a^2 - b^2 = (a - b) (a + b)
G(x) = (5x - 3) (5x+3) +(5x - 3)(x - 15)
= (5x - 3) ((5x + 3) + x - 15)
= (5x - 3) (6x - 12)
G(2)= (5(2) - 3)(6(2) - 12)
= (10 - 3)( 0)
= 0
G(x) = 0 si (5x - 3) (6x-12) =0
Si 5x-3=0 ou 6x-12=0
Si 5x=3 ou 6x=12
si x= 3/5 ou x 12/6 = 2
S ={3/5;2}