Sagot :
Re
f (x) = 9 x² - ( 2 x + 1 )²
f (x) = 9 x² - ( 4 x² + 4 x+ 1 )
f (x) = 9 x² - 4 x² - 4 x - 1
f (x) = 5 x² - 4 x - 1
5 x² - 4 x - 1 = - 1
5 x² - 4 x = 0
x ( 5 x - 4 ) = 0
x = 0 ou 4/5
Re
f (x) = 9 x² - ( 2 x + 1 )²
f (x) = 9 x² - ( 4 x² + 4 x+ 1 )
f (x) = 9 x² - 4 x² - 4 x - 1
f (x) = 5 x² - 4 x - 1
5 x² - 4 x - 1 = - 1
5 x² - 4 x = 0
x ( 5 x - 4 ) = 0
x = 0 ou 4/5