请教我解法！

来源：百度知道 编辑：UC知道 时间：2024/06/09 00:57:54
A farmer wishes to fence off a rectangular field with 1000 feet of fencing.If one side of the field is along the stream and does not require fencing,express the area of the field as a function of its width,y.
请帮忙写出解法，谢谢！

一个农民想用1000英尺长的篱笆围一块矩形的地（rectangular应该是矩形）。如果这块地一边紧靠着小溪，不需要篱笆，请用自变量为宽度的函数表示出地的面积。

s=y*(1000-2y)

Y为河的对应边S=(1000-Y)/2*Y=500Y-Y*Y/2
如果不是 S=1000Y-2Y*Y