数学机经59题求教，谢谢

bradywangs

59. one person has a fence, he uses the fence for a rectangle area, and the length is twice longer than the width.  if he uses the fence for a square, the area will be 400 feet bigger.  how long is the fence?

1. 16

2. 40

3.160

4. 1200

5. 1600

xiaoxiao88

长x宽y

正方形z

x＋y＝2z

xy＋400＝z^2

求2（x＋y）

（x－y）＝400

x＝2y

所以x＝800，y＝400

2400

iselibra

length is twice longer than the width=   X=3Y

所以答案应为 1600

X＋Y＝2Z

X＝3Y

XY＋400＝Z^2

可以解出 Y＝20 X＝60  所以 2（X＋Y）＝160

shuishuiles

define width= w, the total length of fence=x, then:

2w+3(2w)=x

(x/4)^2-3w^2=400

=> x=160