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## #1 2012-07-21 04:01:30

anonimnystefy
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### Differential equations

Post any interesting problems on differential equations here.

Here is one problem:

1)A man starts a business with 100,000\$. Each year his profit is 20%, but he has to pay bills which sum up to 10,000\$ annually. How much money do you predict he will have at the end of year 3 of his business?

Last edited by anonimnystefy (2012-07-21 23:00:38)

The limit operator is just an excuse for doing something you know you can't.
“It's the subject that nobody knows anything about that we can all talk about!” ― Richard Feynman
“A secret's worth depends on the people from whom it must be kept.” ― Carlos Ruiz Zafón

## #2 2012-07-21 18:48:13

bobbym

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### Re: Differential equations

Hi;

I get different answers depending on how I interpret the terms profit and bills. It sounds like bills are paid in a lump sum at the end of each year. Is profit continuous or is it also a lump sum at the end of the year?

In mathematics, you don't understand things. You just get used to them.
90% of mathematicians do not understand 90% of currently published mathematics.
I am willing to wager that over 75% of the new words that appeared were nothing more than spelling errors that caught on.

## #3 2012-07-21 22:40:59

anonimnystefy
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### Re: Differential equations

You can look at both as a sum at the end of the year.

The limit operator is just an excuse for doing something you know you can't.
“It's the subject that nobody knows anything about that we can all talk about!” ― Richard Feynman
“A secret's worth depends on the people from whom it must be kept.” ― Carlos Ruiz Zafón

## #4 2012-07-21 22:59:21

bobbym

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### Re: Differential equations

In mathematics, you don't understand things. You just get used to them.
90% of mathematicians do not understand 90% of currently published mathematics.
I am willing to wager that over 75% of the new words that appeared were nothing more than spelling errors that caught on.

## #5 2012-07-21 23:01:46

anonimnystefy
Real Member

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### Re: Differential equations

Whoops, I have just seen something in the problem. Changed 10% to 20%. Also, you may as well take profit to be made continuously over the year.

The limit operator is just an excuse for doing something you know you can't.
“It's the subject that nobody knows anything about that we can all talk about!” ― Richard Feynman
“A secret's worth depends on the people from whom it must be kept.” ― Carlos Ruiz Zafón

## #6 2012-07-21 23:04:17

bobbym

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### Re: Differential equations

Also, you may as well take profit to be made continuously over the year.

Now, you are talking.

In mathematics, you don't understand things. You just get used to them.
90% of mathematicians do not understand 90% of currently published mathematics.
I am willing to wager that over 75% of the new words that appeared were nothing more than spelling errors that caught on.

## #7 2012-07-21 23:06:26

anonimnystefy
Real Member

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### Re: Differential equations

Yes.

The limit operator is just an excuse for doing something you know you can't.
“It's the subject that nobody knows anything about that we can all talk about!” ― Richard Feynman
“A secret's worth depends on the people from whom it must be kept.” ― Carlos Ruiz Zafón

## #8 2013-01-27 23:12:05

anonimnystefy
Real Member

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### Re: Differential equations

The limit operator is just an excuse for doing something you know you can't.
“It's the subject that nobody knows anything about that we can all talk about!” ― Richard Feynman
“A secret's worth depends on the people from whom it must be kept.” ― Carlos Ruiz Zafón

## #9 2013-01-28 00:01:42

bobbym

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### Re: Differential equations

Hi;

I do not remember what it was.

In mathematics, you don't understand things. You just get used to them.
90% of mathematicians do not understand 90% of currently published mathematics.
I am willing to wager that over 75% of the new words that appeared were nothing more than spelling errors that caught on.

## #10 2013-01-28 00:16:47

anonimnystefy
Real Member

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### Re: Differential equations

Well, there is a nice chance to do it again, if you want.

Last edited by anonimnystefy (2013-01-28 00:17:11)

The limit operator is just an excuse for doing something you know you can't.
“It's the subject that nobody knows anything about that we can all talk about!” ― Richard Feynman
“A secret's worth depends on the people from whom it must be kept.” ― Carlos Ruiz Zafón

## #11 2013-01-28 00:22:44

bobbym

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### Re: Differential equations

I am playing with it right now as you know. I am getting \$141105.94 to the nearest penny. What do you get?

In mathematics, you don't understand things. You just get used to them.
90% of mathematicians do not understand 90% of currently published mathematics.
I am willing to wager that over 75% of the new words that appeared were nothing more than spelling errors that caught on.

## #12 2013-01-28 00:45:38

anonimnystefy
Real Member

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### Re: Differential equations

I am getting \$178101.29.

The limit operator is just an excuse for doing something you know you can't.
“It's the subject that nobody knows anything about that we can all talk about!” ― Richard Feynman
“A secret's worth depends on the people from whom it must be kept.” ― Carlos Ruiz Zafón

## #13 2013-01-28 00:48:54

bobbym

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### Re: Differential equations

Hmmmm, doesn't that seem high?

In mathematics, you don't understand things. You just get used to them.
90% of mathematicians do not understand 90% of currently published mathematics.
I am willing to wager that over 75% of the new words that appeared were nothing more than spelling errors that caught on.

## #14 2013-01-28 00:52:38

anonimnystefy
Real Member

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### Re: Differential equations

The limit operator is just an excuse for doing something you know you can't.
“It's the subject that nobody knows anything about that we can all talk about!” ― Richard Feynman
“A secret's worth depends on the people from whom it must be kept.” ― Carlos Ruiz Zafón

## #15 2013-01-28 01:09:14

bobbym

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### Re: Differential equations

Then I am getting

By the way have you seen my two latest math posts?

http://www.mathisfunforum.com/viewtopic.php?id=18885

http://www.mathisfunforum.com/viewtopic.php?id=18866

In mathematics, you don't understand things. You just get used to them.
90% of mathematicians do not understand 90% of currently published mathematics.
I am willing to wager that over 75% of the new words that appeared were nothing more than spelling errors that caught on.

## #16 2013-01-28 02:29:29

anonimnystefy
Real Member

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### Re: Differential equations

Yes, I have.

The limit operator is just an excuse for doing something you know you can't.
“It's the subject that nobody knows anything about that we can all talk about!” ― Richard Feynman
“A secret's worth depends on the people from whom it must be kept.” ― Carlos Ruiz Zafón

## #17 2013-01-28 02:30:29

bobbym

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### Re: Differential equations

What did you think?

In mathematics, you don't understand things. You just get used to them.
90% of mathematicians do not understand 90% of currently published mathematics.
I am willing to wager that over 75% of the new words that appeared were nothing more than spelling errors that caught on.

## #18 2013-01-28 04:19:37

anonimnystefy
Real Member

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### Re: Differential equations

I alredy know the method for matrix decomposition you've shown in the first one.

I didn't have much time to work on the problems in the dice pdf, but I definitely will, when I have more time...

The limit operator is just an excuse for doing something you know you can't.
“It's the subject that nobody knows anything about that we can all talk about!” ― Richard Feynman
“A secret's worth depends on the people from whom it must be kept.” ― Carlos Ruiz Zafón

## #19 2013-01-28 09:23:37

bobbym

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### Re: Differential equations

Hmmm, so you already knew that one? How about matrix moves? You could not know that one.

In mathematics, you don't understand things. You just get used to them.
90% of mathematicians do not understand 90% of currently published mathematics.
I am willing to wager that over 75% of the new words that appeared were nothing more than spelling errors that caught on.

## #20 2013-01-28 10:32:49

anonimnystefy
Real Member

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### Re: Differential equations

Which one is that?

Last edited by anonimnystefy (2013-01-28 10:33:29)

The limit operator is just an excuse for doing something you know you can't.
“It's the subject that nobody knows anything about that we can all talk about!” ― Richard Feynman
“A secret's worth depends on the people from whom it must be kept.” ― Carlos Ruiz Zafón

## #21 2013-01-28 10:44:29

bobbym

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### Re: Differential equations

In mathematics, you don't understand things. You just get used to them.
90% of mathematicians do not understand 90% of currently published mathematics.
I am willing to wager that over 75% of the new words that appeared were nothing more than spelling errors that caught on.

## #22 2013-01-28 10:50:17

anonimnystefy
Real Member

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### Re: Differential equations

I knew those as well...

The limit operator is just an excuse for doing something you know you can't.
“It's the subject that nobody knows anything about that we can all talk about!” ― Richard Feynman
“A secret's worth depends on the people from whom it must be kept.” ― Carlos Ruiz Zafón

## #23 2013-01-28 10:53:36

bobbym

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### Re: Differential equations

Impossible, I invented that method. Gotcha!

In mathematics, you don't understand things. You just get used to them.
90% of mathematicians do not understand 90% of currently published mathematics.
I am willing to wager that over 75% of the new words that appeared were nothing more than spelling errors that caught on.

## #24 2013-01-28 12:20:39

anonimnystefy
Real Member

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### Re: Differential equations

Nope. That is not correct.

The limit operator is just an excuse for doing something you know you can't.
“It's the subject that nobody knows anything about that we can all talk about!” ― Richard Feynman
“A secret's worth depends on the people from whom it must be kept.” ― Carlos Ruiz Zafón

## #25 2013-01-28 13:16:15

bobbym

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### Re: Differential equations

Yep, I invented the method of getting one element.

In mathematics, you don't understand things. You just get used to them.
90% of mathematicians do not understand 90% of currently published mathematics.
I am willing to wager that over 75% of the new words that appeared were nothing more than spelling errors that caught on.