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## Solving equations system  5-Regular Member

## Solving equations system

According to some web tutorials, I have tried to solve the equations system you can find in the attached figure.

I want to solve the system in order to find variables x and e. All the other variables are defined (you can see defined values also for e and x, they are guess values according to tutorials).

I am not able to find out what is my mistake, if I click on "sol" I see the error "This variable is undefined".

You find also the Mathcad file attached.

Can someone help me?

Sincerely

Stefano Grandi

1 ACCEPTED SOLUTION

Accepted Solutions  13-Aquamarine
(To:mvicenzi)

Two issues here.  One solvable, one not.

Firstly, to use the Find(x) function to solve a system, you must place a Given command before your two equation constraints.

Secondly, before solving anything, always plot your data.  If we rearrange the first equation, putting variable e on the left side (it is separable) and call this e1(x), we can get an idea of how this equation behaves.  Rearranging the second equation in terms of e and calling this e2(x) gives a look at how both equations look and where they may intersect.   They do not intersect.  There is no solution.

3 REPLIES 3  20-Turquoise
(To:mvicenzi)

Hi,

The "Given" keyword needs to be placed after the guess values and before the equations of the solve block.

With the two equations as they stand Fm.c=5 and T=2000 you can set x, e to get 5 and 2000 but not with the same values.

Solve block works Fm.c=5 and T=2 to show you it can work if equations are solvable. Cheers

Terry  5-Regular Member
(To:terryhendicott)

Thank you very much @terryhendicott and @JeffH1!

I solved my issue and I will keep in mind to plot curves before.

Regards  13-Aquamarine
(To:mvicenzi)

Two issues here.  One solvable, one not.

Firstly, to use the Find(x) function to solve a system, you must place a Given command before your two equation constraints.

Secondly, before solving anything, always plot your data.  If we rearrange the first equation, putting variable e on the left side (it is separable) and call this e1(x), we can get an idea of how this equation behaves.  Rearranging the second equation in terms of e and calling this e2(x) gives a look at how both equations look and where they may intersect.   They do not intersect.  There is no solution. 