bonjour
f ( x ) = ( 2 x - 5 )² - 16
développement = 4 x² + 20 x + 25 - 16 = 4 x² + 20 x + 9
2 ) incompréhensible , je suppose qu'il s'agit de la factorisation
f (x) = ( 2 x - 5 - 4 ) ( 2 x - 5 + 4 ) = ( 2 x - 9 ) ( 2 x - 1 )
f ( - 1) = ( - 2 - 9 ) ( - 2 - 1 ) = - 11 * - 3 = 33
( 2 x - 9 ) ( 2 x - 1 ) = 0
x = 9/2 = 4.5 ou 1 /2 = 0.5
f (x) = 16
( 2 x - 5 )² - 16 = 16
( 2 x - 5 )²= 0
x = 5/2
f (x) = 9
( 2 x - 5 )² - 16 = 9
( 2 x - 5 ) ²- 16 - 9 = 0
( 2 x - 5 )² - 25 = 0
( 2 x - 5 - 5 ) ( 2 x - 5 + 5 ) = 0
2 x ( 2 x - 10 ) = 0
x = 0 ou 10/2 = 5
