Please do not post homework questions in this forum. You are supposed to study these things and not copy.
Asking these here is equivalent to copying
Assuming you are electrical engineering student, this answer should be known to you.
It is available in any electrical engineering book.
Hint: Check in the chapter where unbalanced phases are covered.
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Fantastic ideas for a Fantastic World, I make the illogical logical.They put me in cars,they put me in yer tv.They put me in stereos and those little radios you stick in your ears.They even put me in watches, they have teeny gremlins for your watches