bonjour,
B(x)- 79390 =-0.7x²+693.7x-88350.8-79309
-07x²+693.7x-167659.8 =-0.7(x²-991x+239514)
x²-991x+239514=0
Δ=b²-4ac
Δ=991²-4(239514)
Δ=982081-958056
Δ=24025
√Δ=155
x=-b/2a
x=(991+155)/2 =573
x=(991-155)/2=418
x²-991x+239514 peut s'écrire
1(x-573)(x-418)
si -0.7(x-573)(x-418)≥0
x -∞ 418 573 +∞
x-573 - - 0 +
x-418 - 0 + +
(x-573)(x-418) + 0 - 0 +
-0.7(x-573)(x-418) - 0 + 0 -
B(x) ≥79309 si x ∈ [418;573]
