<PRE><B>Question 467046</B>
Jack builds a rectangular animal pen using 20 fence posts placed every 4 feet along the perimeter of the pen.What is the greatest possible area o the animal pen? 
---
Using 20 posts you could get a perimeter of 4*20 = 80 ft.
Perimeter = 2[length + width]
length + width = 40
L =  40-W
---
Area = LW
Substitute to get:
A = (40-W)W
---
Quadratic form:
Area = 40W-W^2
-----
Maximum Area occurs when W = -b/(2a) = -40/(-2*1) = 20
Then L = 40-20 = 20
---
Max area = 400 sq. ft which gives a square which is also a rectangle.
=========================
Cheers,
Stan H.
==================</PRE>