1.设一年中修了x公顷蔬菜大棚,总费用为(27000x+9000x^2)
75000x-(27000x+9000x^2)=60000
3x^2-16x+20=0
(x-2)(3x-10)=0
x=2或x=10/3
一年中修了2公顷或10/3公顷蔬菜大棚
2.增加的效益相同,但修建10/3公顷大棚多占地,多浪费劳动力.
3.修建3公顷大棚的效益为:75000*3-(27000*3+9000*3^2)=63000元
4.设收益为y
y=75000x-(27000x+9000x^2)
=-9000x^2+48000x
=-9000(x^2-16x/3)
=-9000[x^2-16x/3+(8/3)^2-(8/3)^2]
=-9000[(x-8/3)^2-64/9]
=-9000(x-8/3)^2+6400
当x=8/3时y值最大
所以修建大棚的面积越大收益不一定越大,当超过8/3公顷时面积越大收益也越小.