## KJ4UTS one year ago A farmer wants to fence in a rectangular field that encloses 3600 square feet. One side of the field is along a river and does not require fencing. The fencing costs \$3.50 per foot. Express the total cost C(x) of the fencing (in dollars) as a function of x. Please explain. Thank you!

1. KJ4UTS

2. anonymous

Can you answer the following? Write a formula for the length of the fence (using x & y).

3. KJ4UTS

Would that be 3600=x+x+y? The last one C(x)=3.50(x+3600/x) but I am not sure.

4. anonymous

It can be rewritten as 3600 = 2x + y. How would you write y in terms of x?

5. KJ4UTS

3600-2x=y?

6. anonymous

correct

7. KJ4UTS

So does that make the answer the third one down C(x)=3.50(2x+3600/x)?

8. KJ4UTS

and is there a number that can be plugged in to check to see if the function is correct?

9. anonymous

I'm sorry I knew how to do this, but at the moment I'm blanking out. If it comes to me, I'll try to post.

10. Michele_Laino

Hint: the are of your field is: xy=3600, so we have: y=3600/x then the perimeter $$\large p$$ that has to be fenced is: $\Large p = x + x + y = 2x + \frac{{3600}}{x}$

11. Michele_Laino

area*

12. Michele_Laino

@KJ4UTS

13. anonymous

I should have asked earlier what is the formula for the area, to which the answer is A = l x w => 3600 = x(y) So y = 3600/x So I think that you are correct Perimeter = 2x + (3600/x) So cost = 3.5 [2x (3600/x)] Can someone verify this?

14. Michele_Laino

so, we have: $\Large C\left( x \right) = 3.50p = ...?$

15. Michele_Laino

so, what is the right option?

16. KJ4UTS

@Michele_Laino the right option looks like the third one down C(x)=3.50(2x+3600/x)?

17. Michele_Laino

correct!

18. KJ4UTS

Thank you :)

19. Michele_Laino

:)