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f(x) = .3 x² - 6 x - x + 2 - 4 + 2 x
f(x) = 3 x² - 5 x - 2

(3 x - 1 ) ( x -2) + 2 ( - 2 + x)
( x -2 ) ( 3 x - 1 + 2)
( x -2) ( 3 x + 1)

f(0) = (-1) ( - 2) - 4
f(0) =  2 - 4 =  -2

f(x) = 0
on part de la forme factorisée

( x - 2) ( 3 x +1) = 0
soit x - 2 = 0 et x = 2
soit 3 x + 1 = 0
      3 x = - 1 et x = - 1/3

f(x)  = - 2

( x - 2) ( 3 x + 1) = - 2
(x - 2) ( 3 x + 1) - 2 = 0
( x -2) ( 3 x +1 - 2) = 0
(x -2) ( 3 x - 1) = 0
soit x -2 = 0 et x = 2
soit 3 x - 1 = 0
3 x = 1
x = 1/3