bonjour
A (x) = ( x + 1 ) ( 2 - x ) - 2 ( x + 1 ) ( 2 x + 3 )
A (x) = 2 x - x² + 2 - x - 2 ( 2 x² + 3 x + 2 x + 3 )
A (x) = - x² + x + 2 - 4 x² - 6 x - 4 x - 6
A ( x) = - 5 x² - 9 x - 4
A (x) = ( x + 1 ) ( 2 - x - 4 x - 6 )
A (x ) = ( x + 1 ) ( - 5 x - 4 )
A (2) = ( 2 + 1 ) ( - 10 - 4 ) = 3 * - 14 = - 42
tu fais pour A ( - 1 )
A (x) = 0
( x + 1 ) ( - 5 x - 4 ) = 0
⇔ x = - 1 ou - 4/5
A (x) = - 4
- 5 x² - 9 x - 4 = - 4
- 5 x² - 9 x - 4 + 4 = 0
- 5 x² - 9 x = 0
- x ( 5 x + 9 ) = 0
⇔ x = 0 ou - 9/5
A (x) = - 5 x²
- 5 x² - 9 x - 4 = - 5 x²
- 5 x² + 5 x² - 9 x = 4
- 9 x = 4
x = - 4/9
