bonjour
partie A = lecture graphique donc tu as tout sur le graphique .
f (x) = ( x + 1 ) ( 6 - 2 x )
g (x) = x² + 2 x + 1
f (x) = 6 x - 2 x² + 6 - 2 x = - 2 x² + 4 x + 6
2. f (x) = - 2 ( x - 1 )² + 8
f (x) = - 2 ( x² - 2 x + 1 ) + 8
f (x) = - 2 x² + 4 x - 2 + 8 = - 2 x² + 4 x + 6
3. ( x + 1 ) ( 6 - 2 x ) = 0
x = - 1 ou 3
( x + 1 ) ( 6 - 2 x ) = x² + 2 x + 1
6 x - 2 x² + 6 - 2 x = x² +2 x +1
- 2 x² - x² + 4 x - 2 x = 1 - 6
- 3 x² + 2 x = - 5
- 3 x² + 2 x + 5 = 0
Δ = 4 - 4 ( - 3 *5 ) = 4 + 60 = 64 = 8 ²
x 1 = ( - 2 - 8 ) / - 6 = - 10 /- 6 = 5/3
x 2 = ( - 2 + 8 ) /-6 = 6 /- 6 = - 1
