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11-Garnet
September 4, 2022
Solved

Math equation solving problem

  • September 4, 2022
  • 3 replies
  • 3180 views

Hi experts,

 

Can anyone know how to solve this problem?

it seems the equation is too complicated, so the system can't solve it.

any other methods that can solve this issue?

_9593174_0-1662301645340.png

 

Best answer by LucMeekes

LucMeekes_0-1662381157480.png

Then:

LucMeekes_1-1662381174803.png

and:

LucMeekes_2-1662381195802.png

 

Success!
Luc

3 replies

25-Diamond I
September 4, 2022

You sure should attach your worksheet, not just show a pic.

What is the error message you get?

Has the variable x not been assigned a value before anyway? If you did, that would throw an error.

On first sight you may end up with a biquadratic equation of sixth order. Its quite possible that Mathcad either is not able to solve it symbolically or (more like, I guess), that the solution Mathcad can come up with is too large and cannot be displayed. In the latter case you still can assign the solution to a function in Q and k and use that function in later calculations.
It may also be the case that Mathcad is not able to display the full solution vector (I assume a 6 x 1 vector) but is able to display all or most of its entries singly one by one.

You may also parametrize a solve or a root call so you can create a (numerical) function in Q an k.

So there a quite some possibilities to deal with the problem. While it might be possible to let Mathcad show you the symbolic solution (at least the one with a positive, real value which as I guess is what you are interested in), its highly likely, that you don't really need the symbolic expression.

 

Are you sure that you really need a symbolic solution? If Q and k are known, you may try a solve block or the root function as well. After all you followed the symbolic solve by a numeric equal sign. If Q and/or k are unknowns, this would yield an error in any case.

 

21-Topaz II
September 4, 2022

Hi,

The error message states make a function

Capture.JPG

So turn it into a function then use the function

Capture2.JPG

25-Diamond I
September 4, 2022

Your function K.3 does not need the third argument x as x is the variable which the expression is solved for and so should not appear at the (too large) solve expression.

In another thread I got the impression that the OP was only interested in real and positive solutions. In the symbolic symbolic solve vector

Werner_E_0-1662333224330.png

this seems to be the very first entry. Wen can isolate it and Mathcad even is able to display it

Werner_E_2-1662333951439.png

"simplify" doesn't do a great job on this

Werner_E_1-1662333270150.png

But as I guess that Q and k will only take real values, we can talk Mathcad into simplifying the expression a bit further

Werner_E_3-1662334040749.png

Now this function can be used numerically at will

Werner_E_4-1662334079484.png

 

I can be proven wrong but I still think that a pure numerical approach without using the symbolic "solve"  would be more appropriate.

Maybe like this:

Werner_E_5-1662334301476.png

 

LucMeekes23-Emerald IVAnswer
23-Emerald IV
September 5, 2022

LucMeekes_0-1662381157480.png

Then:

LucMeekes_1-1662381174803.png

and:

LucMeekes_2-1662381195802.png

 

Success!
Luc

25-Diamond I
September 5, 2022

Nice! 👿

Maybe it should be explained to @J_power  that you are using Mathcad 11 and MC11 is able (or could be made able) to display larger symbolic results.