Forgetting my Math...Any help?

[PricklyPete]

I feel like a collossal idiot. It has been a very long time since I was in a math class doing simple Algebra and I am drawing a complete blank on how to go about solving this problem. I developed an equation that produces the correct answer every time:

[ B/(1-A) ] + [ D/(1-C) ]

The problem is that this does not fit into my algorithm very well (for reasons that would take too long to explain). I came up with a separate equation that produces almost the same value each time (the discrepency always seems to show up after the 3rd or 4th decimal place). The new equation is this:

[ 1/(1-AxB) ] x [1/(1-CxD) ]

While the numerical examples always come really, really close, I wanted to prove that they were the same mathmatically before I use the second equation in my algorithm. This is where I forget how to do this. Where do I start? At first I set the to one equal to 0 and tried to solve for the second one...but I think I am making a huge blunder there...I don't believe I can do that. If anyone can give me a hint in the right direction, it would greatly appreciated.

I feel sooo stupid right now!

 

[agnitrate]

Originally posted by: PricklyPete

Where do I start? At first I set the to one equal to 0 and tried to solve for the second one...but I think I am making a huge blunder there...I don't believe I can do that.

First off, don't feel stupid. Math can be frustrating at times.

Secondly, I'm not sure exactly what you want to do with the formula. You can't solve it unless you set it equal to something (like 0 as you stated) but this has to be implied within the algorithm you are using. What does this function represent?

The only thing you can do aside from solving it is get a common denominator. This would give you as follows :

B - BC + D - DA
-----------------------
(1 - A) * (1 - C)

Maybe you can explain what you're trying to do here and it will be more clear.

-silver

 

[PricklyPete]

I am thinking the two equations are the same, but I am not sure. What I am wanting to do is prove that the first equation is actually equal to the second equation. How do I go about doing that.

Thanks again for any help. Let me know if I am not providing enough detail.

 

[Woodchuck2000]

The equations are simply not the same. That's why you get different answers and why it can't be proved mathematically.

 

[Mday]

first of all, those 2 equations are not the same.

 

[notfred]

Yeah, the reason you can't prove that they're equivelent is because they're not. If they were the same, you wouldn't be getting different answers for both of them.

 

[PricklyPete]

Thanks. I was hoping the reason the answers weren't perfectly the same was because of round-off errors. Last question: how would I go about proving that the two equations are not the same?

 

[agnitrate]

Originally posted by: PricklyPete
Thanks. I was hoping the reason the answers weren't perfectly the same was because of round-off errors. Last question: how would I go about proving that the two equations are not the same?

Set them equal to each other and then you should have a contradiction.

-silver

 

[PricklyPete]

Thanks.

 

[GermyBoy]

Originally posted by: PricklyPete
Thanks.

YW

 

[oboeguy]

The easiest way to show they are not the same is via counter-example. Consider B=D=0, with A and C anything. The first formula (note there's no equal sign ==> formula, not equation ) gives a value of zero, while the second a value of one. QED.

BTW, I really dislike it when folks are embarrased by "not remembering" or "not being good at" math. Don't be silly! Everyone forgets things if those things are used every day. There's no need for shame.