Bonsoir,

Développer f(x)

f(x)= 9x²+12x+12x+16 - (4x²-2x-2x+1)

f(x)= 9x²+24x+16-4x²+4x-1

f(x)= 5x²+28x+15

Factoriser f(x):

f(x)= (3x+4-2x+1)(3x+4+2x-1)

f(x)= (x+5)(5x+3)

Résoudre f(x)= 0

(x+5)(5x+3)= 0

x+5= 0  ou  5x+3= 0

x= -5                x= -3/5

S= { -5; -3/5 }

Résoudre f(x)= 15

5x²+28x+15= 15

5x²+28x+15-15= 0

5x²+28x= 0

x(5x+28)= 0

x= 0  ou x= -28/5

S= { -28/5 ; 0 }