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Best answer by Werner_E

I agree with Luc that a numeric solution should suffice here.

 

Just for fun you may look in the attached sheet to see how to convince the symbolics to solve the equation and als to just give us the positive solution.

You have to know that the symbolics does not know anything about units and so it does not know what mm might be. By telling it via the "assume" command that mm>0 its willing to solve.

B.jpg

2 replies

L
LucMeekes23-Emerald IV
23-Emerald IV
March 21, 2019

I don't know what the error message for the symbolic solve says, but, would 7.83 mm do fine?

Instead of symbolic solve, you can use a numeric solve: the root function.

See attachment.

 

Success!
Luc

 

Note that the symbolic solver of Prime does NOT know about units. It treats them as undefined variables. In cases (as yours) where the unitsare balanced, or cancel out, that can still work fine. There are many cases where it doesn't.

In general, when you want to find a symbolic solution, first solve your problem fully symbolically, so without defining any values (or as little as possible). You can assign the result of the symbolic solution to a function (with any variables you need to use as parameters) and use that function to calculate the result.

    G
    geonicolae211-VisitorAuthor
    1-Visitor
    March 21, 2019

    I don't know what the answer should be, but it's seems to be a possible answer so I think it's ok.

     

    Thank you.

    W
    Werner_E25-Diamond IAnswer
    25-Diamond I
    March 22, 2019

    I agree with Luc that a numeric solution should suffice here.

     

    Just for fun you may look in the attached sheet to see how to convince the symbolics to solve the equation and als to just give us the positive solution.

    You have to know that the symbolics does not know anything about units and so it does not know what mm might be. By telling it via the "assume" command that mm>0 its willing to solve.

    B.jpg

      G
      geonicolae211-VisitorAuthor
      1-Visitor
      March 24, 2019

      Thank you very much.

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