# Stuck on a problem

• Aug 28th 2008, 10:45 AM
rm1991
Stuck on a problem

Zeta plans to fence off a rectangular field along the bank of a river; no fence is needed along the river. Fencing cost \$2 per foot for the ends and \$3 per foot for the side parallel to the river. Zeta's budge is \$900

1. Let x be the length of the ide of the field that lies along the river. Explain why the formula A(x) = x(225 - .75x) describes the area of the field.

I know that the area of a rectangle would be length * width... which would explain where x is coming from but im not sure where the stuff inside the parenthesis are coming from. I think .75 would mean that the width would be 75% of the length but not sure how to get 225.
• Aug 28th 2008, 11:28 AM
11rdc11
Hi

let me draw a pic for you and see if this makes it easier to understand

1000000000001
1000000000001
2y 1000000000001 2y
1000000000001
1111111111111

3x

ok now set up a formula for the perimeter

\$\displaystyle 4y + 3x = 900\$

\$\displaystyle y = 225 - .75x\$

Now area is xy so

\$\displaystyle A= x(225 - .75x)\$

Hope this helps
• Aug 28th 2008, 11:36 AM
rm1991
yes... i see it. Many thanks :)