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#26 2013-03-11 06:35:36

BarandaMan
Guest

Re: Derive an Equation....Please Help! :)

BarandaMan wrote:

I get it to equal 6 funnily enough, not 3 xD! tongue

I didn't have the WHOLE expression over alpha (which =2), I left that out by mistake, sorry! So it does in fact equal 3! Yay!

#27 2013-03-11 06:39:37

bob bundy
Moderator

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Re: Derive an Equation....Please Help! :)

Oh yes.  I had an expression for alpha e too and made the same mistake!

Now you see the value of the number values trick.  Not only did it tell you there was a mistake; but it also helped you to spot what it was.

Bob


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

#28 2013-03-11 06:41:14

BarandaMan
Guest

Re: Derive an Equation....Please Help! :)

Ok,

my other solution for e, which I hope is what you got, is:

e= ((alpha*A)  + g* - ((b* + gammaA - b)/gamma)) / alpha (the whole thing over alpha)

big_smile

#29 2013-03-11 06:42:06

BarandaMan
Guest

Re: Derive an Equation....Please Help! :)

bob bundy wrote:

Oh yes.  I had an expression for alpha e too and made the same mistake!

Now you see the value of the number values trick.  Not only did it tell you there was a mistake; but it also helped you to spot what it was.

Bob

It is incredible, thank you so much for this. I will definitely try create my own in the future for similar problems to check my work! big_smile

#30 2013-03-11 07:05:06

bob bundy
Moderator

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Re: Derive an Equation....Please Help! :)

Actually I didn't (post 28) .  But that doesn't mean you are wrong (what did the spreadsheet give you?).

Why so many answers to this? :

an expression for 'e', without using 'e','r', or 'a*'....

Well there is a good reason why this happened.

There are 4 equations and 12 variables.  For the first part you were asked to get one equation with 3 variables forbidden.  It worked like this:

4 equations and 12 variables ... eliminate e gives

3 equations and 11 variables ... eliminate r gives

2 equations and 10 variables ... eliminate a* gives

1 equation and 9 variables.

So we have lost the three variables exactly as required.  There's only one answer. (with maybe a bit of re-arranging)

For part two you are asked for one equation with two variables forbidden ( 'e' doesn't count because that's the one we are trying to make)

4 equations and 12 variables ... eliminate 'r'

3 equations and 11 variables ... eliminate a*

2 equations and 10 variables.

We've eliminated the forbidden variables but still have two equations.  You can still eliminate a variable if you want and get a correct equation.  But which one to eliminate?  There's lots of choices so lots of answers.  Your teacher is going to have lots of work checking each different answer to see if it works.  smile  Unless the question is worded in such a way that it steers you towards one answer rather than another.

Bob

Last edited by bob bundy (2013-03-11 07:07:34)


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

#31 2013-03-11 23:44:20

BarandaMan
Guest

Re: Derive an Equation....Please Help! :)

Thank you for the explanation, that really helps. Actually there is no other question except for the 'derive e' line! tongue

#32 2013-03-11 23:49:35

bob bundy
Moderator

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Re: Derive an Equation....Please Help! :)

Happy to have been of help.  As for the many answers, we'll just have to see.

Bob


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

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