bonjour
f (x) = ( x + 3 ) ( 5 - 10 x )
f ( x) = 5 x - 10 x² + 15 - 30 x
f ( x) = - 10 x² - 25 x + 15
f (x) = 0
Δ = ( - 25 )² - 4 ( 5 * - 30 )
Δ = 625 + 600 = 1 225 = 35 ²
x ₁ = ( 25 + 35 ) / - 20 = - 60/20 = - 3
x ₂ = ( 25 - 35 ) / - 20 = - 10 / - 20 = 1 /2
donc f (x) = 0 pour x = - 3 et 1/2
f (x) = 15
- 10 x² - 25 x + 15 = 15
- 10 x² - 25 x + 15 - 15 = 0
- 10 x² - 25 x = 0
5 x ( - 2 x - 5 ) = 0
x = 0 ou - 5 /2
