Math Is Fun Forum
  Discussion about math, puzzles, games and fun.   Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ • π ƒ -¹ ² ³ °

You are not logged in.

#1 2012-08-03 00:37:28

draketcg
Member
Registered: 2012-08-03
Posts: 2

Need to find the smallest value for a rectangle with 40m² area.

Hi.
It's basically this, I got some questions in this style and I can't find a way to solve it. This is one of them:

"Paul has enough materials to build up a 24m fence. He wants to surround a 40m² rectangular terrain. Is that possible? If not, what's the maximum rectangular area Paul can reach with those materials?"
Please show your work.

Thanks in advance!

Offline

#2 2012-08-03 01:09:57

bob bundy
Moderator
Registered: 2010-06-20
Posts: 6,269

Re: Need to find the smallest value for a rectangle with 40m² area.

hi draketcg

Welcome to the forum!

If you call the length x then the width must be (24 - 2x)/2 = 12 - x

So the area is x(12-x)

So the question is, can you make that equal to 40 ?

If you try to solve that using the quadratic formula:

There are no real values of x to solve that square root so it would seem it is not possible.

To find the biggest area I'll make a graph first :

You can see from the graph ( at the end ) that the maximum is below 40, so that confirms the statement above.

Quadratics are symmetrical so the maximum will be at x = 6

Or use calculus to find the maximum.

So biggest area = 6(12-6) = 36

Bob

View Image: draketcg.gif

You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

Offline

#3 2012-08-03 01:21:31

draketcg
Member
Registered: 2012-08-03
Posts: 2

Re: Need to find the smallest value for a rectangle with 40m² area.

Sweet. It's easy to understand if you explain this way, thanks a lot!

Offline

#4 2012-08-03 01:26:48

bob bundy
Moderator
Registered: 2010-06-20
Posts: 6,269

Re: Need to find the smallest value for a rectangle with 40m² area.

You're welcome.

If you have more like this, see how far you can get on your own, and post again if you get stuck.

Bob


You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

Offline

Board footer

Powered by FluxBB