总耗油量
=【(1/14400)X^3-(1/360)X+3】×（120/x）
= x^2/120 -1/3 +360/x
= x^2/120 + 180/x + 180/x -1/3
>=3*三次开方（x^2/120 × 180/x × 180/x）-1/3
=9*（10的三次开方）- 1/3
当且仅当x^2/120=180/x时等号成立
此时x=6×（100的三次开方）真的我没看懂。好吧`````````````我发图给你``````````````````````````````````我看到了黑屏。我再发一次`````