math questions

来源：百度知道 编辑：UC知道 时间：2024/06/21 00:07:11
a rectangular enclosure is to be bulit with 3 sides made out of redwood fecing at a cost of $7 per runjning foot, and the fourth side made out of cement blocks at a cost of $14 pe running foot. $1690 is available for the project. the maximum possible aea of such an enclosure is closest to?the length of the side with cement blocks is closest to?
i need steps. thanks~

suppose the fourth side made out of cement blocks is lenght x,and the other two sides is y
14x+28y=1690
need the xy is maximum
according the expressions (a+b)/2≥ab when a=b,(a+b)/2=ab
so 28x=1690 56y=1690
the maximum possible aea of such an enclosure is closest to 42.678