I'm lost, really lost. I can not make this work. I tried very hard, but everything seems that launches an error or not works as supposed (based on the examples that I saw).
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Another test:
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I hope someone can help, not only giving me a solution, also explaining me why the examples works and my code not. Thanks in advance!

Examples here:
http://software-solutions-online.com...ing-equations/
https://msdn.microsoft.com/en-us/lib.../ff821988.aspx