Starting from the preceding line:
Move to the numerator of (commutative property of multiplication).
Move to the far right of the expression (commutative property of multiplication).
Multiply by .
I assume , in which case .
That's the way you do to find an expression of the form for a fraction of the
The only weird thing is why you people use the letter "j" to denote what the huge majority
of mathematicians in the world denote by "i" = the imaginary unit, though I found that
in a very old book...