bonjour
f (x) = - 3 x² - 24 x + 27
f (x) = - 3 [ ( x + 4 )² - 25 ) ]
f (x) = - 3[ ( x + 4 - 5 ) ( x + 4 + 5 )]
f (x) = - 3 ( x - 1 ) ( x + 9)
f (x) = - 3 ( x² + 9 x - x - 9 )
f (x) = - 3 x² - 27 x + 3 x + 27
f ( x) = - 3 x² - 24 x + 27
f (0) = 27
f ( -3) = - 3 ( - 3)² - 24 *-3 + 27 = - 81 + 72 + 27 = 18
tu fais le calcul pour f ( - 4)
- 3 x² - 24 x + 27 = 27
- 3 x² - 24 x + 27 - 27 = 0
- 3 x ( x + 8 ) = 0
x = 0 ou - 8
f (x) = 0
- 3 ( x - 1) ( x + 9) = 0
( - 3 x + 3 ) ( x + 9) = 0
x = 1 ou - 9
