bonjour,
f (x) = - 2 x² + 8
f ( 3) = - 2 *9 + 8 = - 18 + 8 = - 10
f ( - 8) = - 2 ( - 8)² + 8 = - 64 + 8 = - 56
f ( 2.5) = - 2 ( 2.5)² + 8 = - 12.5 + 8 = - 4.5
f ( - 0.1) = - 2 ( - 0.1 )² + 8 = - 0.02 + 8 = 7.98
f ( √5 ) = - 2 ( √5)² + 8 = - 10 + 8 = - 2