a_ (x+7) ²=(x+7) (3x+4)
(x+7) (3x+4) - (x+7)² = 0
3x²+4x+21x+28 - ( x² + 2.x.7+ 7²) = 0
3x²+4x+21x+28 - x² -14x - 49 = 0
2x²+11x -21 = 0
calcule le discriminant
delta = 11² - 4.2.(-21)
delta = 289
delta > 0 alors lequation admet deux solutions :
x1 =( -11 - racine de 289 )/4= -7
x2 = ( -11 +racine de 289)/4= 3/2
s = { -7 ; 3/2}
