Thanks for reply.
About j := i
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I know that it can be expressed in SMath another way, for ex. like this:
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But, It is very helpful that it can be represented in result (answer) just like this:
Z := (0 − j*50) Ω = 50*e^-j90° Ω
or like this
Z := (0 − j*50) Ω = 50∠−90° Ω