设收益为y元,大棚面积为x公顷,则
y=75000x-27000x-9000x^2=48000x-9000x^2=-1000(9x^2-48x)
=-1000[(3x-8)^2-64]
收益当大棚面积为8/3公顷时,收益最大为64000元.