Appearing error with -i instead of units

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I'm attaching the screen and file. 

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Unfortunately I only see the screen shot.

Because of a severe bug in this forum you have to put Mathcad files in a zip (or any other) archive before you are able to attach them here.

"i" ist not "appearing" instead of units but additionally. The value under the root is negative and so the result is a complex number, consisiting of a real and an imaginary part. "i" ist the imaginary unit.

If you did not expect that kind of result, you'll have to check the values involved.