bonjour
f (x) = ( x + 2 )² - 9
f ( x) = x² + 4 x + 4 - 9 = x² + 4 x - 5
f ( x) = ( x + 2 - 3 ) ( x + 2 + 3 )
= ( x - 1 ) ( x + 5 )
f (x) = - 9
( x + 2 )² - 9 = - 9
( x + 2 )² - 9 + 9 = 0
( x + 2 )² = 0
x = - 2
f ( x) = 0
( x - 1 ) ( x + 5 ) = 0
x = 1 ou - 5
f ( x ) = - 5
( x + 2 )² - 9 = - 5
( x + 2 )² - 9 + 5 = 0
( x + 2 )² - 4 = 0
( x + 2 - 2 ) ( x + 2 + 2 ) = 0
x ( x + 4 ) = 0
x = 0 ou - 4
