Bonjour,
-x + 8 = -5x
5x - x = -8
4x = -8
x = -8/4
x = -2
4x^2 + 16x = 6(4x + 10)
4x^2 + 16x - 24x - 60 = 0
4x^2 - 8x - 60 = 0
4(x^2 - 2x - 15) = 0
x^2 - 2x - 15 = 0
On pose x = X + 1 :
(X + 1)^2 - 2(X + 1) - 15 = 0
X^2 + 2X + 1 - 2X + 2 - 15 = 0
X^2 - 12 = 0
X^2 = 12
X = V12 ou X = -V12
X = 2V3 ou X = -2V3
x = X + 1
x = 2V3 + 1
Ou
x = -2V3 + 1