bonjour
f(x) = - 2 ( x - 1)² + 18
f(x) = - 2 ( x² - 2 x + 1) + 18
f(x) = - 2 x² + 4 x - 2 + 18 = - 2 x² + 4 x + 16
f(1) = - 2 + 4 + 16 = 18
f(x) = 0
- 2 x² + 4 x + 16 = 0
Δ = 4² - 4 ( - 2 * 16) = 16 + 128 = 144 = 12 ²
x 1 = ( - 4 - 12) / - 4 = - 16/- 4 = 4
x2 = ( - 4 + 12) / - 4 = 8/-4 = - 2
S ( - 2 ; 4 )