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J
J_power11-Garnet
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

W
Werner_E25-Diamond I
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.

 

T
21-Topaz II
terryhendicott21-Topaz II
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

    W
    Werner_E25-Diamond I
    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

     

      L
      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

      W
      Werner_E25-Diamond I
      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.

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