Math Is Fun Forum

lakeheadca

Member

Registered: 2010-01-31

Posts: 37

Create an equation

A rectangle or square with perimeter 100cm, area 25 cm² what will be the equation.
is it
w²+25w+100
w²+50w+25
w²+25w-100
the third option i dont remember.
Please explaine
thank you.

Last edited by lakeheadca (2010-06-18 11:04:26)

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Create an equation

Hi;

Start by using the equations for A and P.

P = 100 = 2L + 2W

A = 25 = L * W

Solving from the first equation:

L = 100 - 2W = 50 - W

Can you finish from here?

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

lakeheadca

Member

Registered: 2010-01-31

Posts: 37

Re: Create an equation

Please can you explain that actually what this question is asking.  What this equation will do. I still don't know how to come up the equation. Am I finding length which is equal to this function. It is quadratic equation, so there are two W??
I am not good in math. Sorry.

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Create an equation

Hi lakeheadca;

We have the 2 equations:

P = 100 = 2L + 2W

A = 25 = L * W     These are easy. But not easy to solve for all those variables. So we try to eliminate one. We solve for the L from the first equation.

L = 100 - 2W = 50 - W

25 = L * W   Substitute 50 - W for L

25 = ( 50 - W ) W  This is a quadratic, so expand it.

25 = 50W - W^2 

W^2 - 50 W + 25 = 0

Now solve by the quadratic formula. Are you Okay with this? Or do you need more help? After you get the answer I will go over the equations with you.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.