Following a comment here: Solving cubic and quartic equations with Excel the Quartic and CubicC User Defined Functions (UDFs) have been amended to fix a problem occurring with some combinations of coefficients.
The updated spreadsheet (including full open source code) can be downloaded from: Polynomial.zip
As well as functions to solve Quartic, Cubic and Quadratic equations analytically the spreadsheet includes an iterative method that will solve polynomial functions of any order, using the Jenkins-Traub method, and a function to evaluate polynomial functions of any order.
Newton Excel Bach, not (just) an Excel Blog 
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I cannot find the words to thank you for your help in solving polynomials equations, it was a real headache and with the help of your download every thing went smooth
Thanks & Best Regards
Imad Al-Satary
Sales Manager
Jordan House for Modern Technology
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Thanks for the comments.
You might also like to check you have the latest version:
https://newtonexcelbach.wordpress.com/2014/08/14/solving-polynomials-update/
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The second I click enable editing it breaks apart and fails, any idea how to solve that?
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No, but if you provided some details I might. What breaks apart and fails exactly? Windows or Mac, and which version? What version of Excel? Any other information that might be relevant?
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I’m using windows, and so whatever links or formula’s that are used instantly break once clicking on “enable editing”. It’s as though enable editing wipes away the custom formula’s and functions set in the code so each fails to run as it doesn’t know the functions anymore.
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I’m not sure why you are getting an “enable editing” box. If you save the zip file to your local drive, and extract the polynomial.xlsb file, then open that, you should get a box to enable macros, and if you click that, the functions should work.
Also do you get the same problem with other files, or just this one?
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Anytime a windows user downloads an excel file it automatically puts it in a protected state where no cell can be edited nor any functions can be edited. Until I click “enable editing” from a bar on the top of my excel page I literally cannot do anything besides view the sheets. Its standard practice for Excel 2016.
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After you download – do a right click on the file in the downloads folder – choose properties – select unblock
Alfred
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Thanks for that Alfred.
It seems the reason I don’t get the “enable editing” box (even with other peoples’ files) is because I always un-zip and open using the File Manager “Total Commander”, which seems to do the un-block automatically, although I still have to “enable content”, unless I copy to a “trusted location”.
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Thanks Excel1star!
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Joshua – did the Excel1star solution work for you?
If so, good, but for future reference and other downloads:
After you click “enable editing” you should immediately get a similar box “enable content”, and after you click that the user defined functions and macros should work.
If you don’t get the “enable content” box, and the functions aren’t working then:
In Excel, go to File-Options-Trust Center, click on Trust Centre Settings, then Macro Settings and select “Disable all macros with notification”, and also tick “Trust access to the VBA project object model”
After you do that you should get the “enable content” box, whether “enable editing” appears or not. You can also set up a “trusted location”, and any files copied there should have editing and macros enabled automatically, but you probably don’t want to do that with download files until you have checked them out.
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