salut je pense que j'ai trouve la réponse:
1/ f(x)>d(x)
-500000/x + 35000 > -750x + 45000
-50000+35000x>-750x²+45000x
750x²-10000x-50000>0
2/ f(x)<d(x)
-500000/x + 35000 < -750x + 45000
-500000+35000x<-750x²+45000x
750x²-10000x-500000x<0
3/ 750x²-10000x-500000x<0
150x²-2000x-100000<0
15x²-200x-10000<0
3x²-40x-2000<0
et 750x²-10000x-500000x>0
150x²-2000x-100000>0
15x²-200x-10000>0
3x²-40x-2000>0
4/ a/ (x +20) (3x - 100)=3x²-100x+60x-2000=3x²-40x-2000
b/ f(x) > d(x)
750x²-10000x-50000>0
3x²-40x-2000>0
(x +20) (3x - 100)>0
