bonjour
f (x) = - 1 / 2 x² + 8 x + 18 = - 0.5 x² + 8 x + 18
f (x) = - 1 /2 ( x - 8 )² + 50
f (x) = - 1/2 ( x² - 16 x + 64 ) + 50
f (x) = - 0.5 x² + 8 x - 32 + 50 = - 0.5 x² + 8 x + 18
f (x) = - 1/2 ( x - 1 8 ) ( x + 2 )
f (x) = ( - 0.5 x + 9 ) ( x + 2 )
f (x) = - 0.5 x - x + 9 x + 18 = - 0.5 x + 8 x + 18
