Bonsoir
f (x) = x² - ( 5 x + 2 )²
a. f (x) = x² - ( 25 x² + 20 x + 4 ) = x² - 25 x² - 20 x - 4 = - 24 x² - 20 x - 4
b . f (x) = ( x + 5 x + 2 ) ( x - 5 x - 2 ) = ( 6 x + 2 ) ( - 4 x - 2 )
c. f ( 0) = - 4
f ( 2 √2) = - 24 ( 2 √2)² - 20 ( 2 √2) - 4
f ( 2 √2) = - 24 * 8 - 40 √2 - 4 = - 192 - 40 √2 - 4 = - 196 - 40 √ 2
f ( -5) = - 24 ( - 5 )² - 20 * - 5 - 4 = - 600 + 100 - 4 = - 504
f (x) = 0
( 6 x + 2 ) ( - 4 x - 2 ) = 0
x = - 2/6 = - 1 /3 ou 2/4 = 1/2
