This is part of larger program involving functions that preserve order over the positive reals.
But I'm trying to show that
∀x,y∈C |xy|≤|x||y|
My work:
Let x=ax+bxi, Let y=ay+byi, ℜ=Real Part,ℑ=Imaginary Part
|xy|=|eln(x)y|=|eln(ax+bxi)(ay+byi)|=eℜ(ln(ax+bxi))ay−ℑ(ln(ax+bxi))by
This needs to be compared to |x||y|=eln(√a2x+b2x)√a2y+b2y
But i'm at a loss for how to compare these two objects. I do have some intuition though, for one as by→∞ the first expression tends towards 0, while the bottom expression grows without bound.
Answer
i−i=exp(−ilni)
Take the principal branch of the logarithm, then lni=iπ/2, thus
i−i=exp(π/2)
and the requested inequality is satisfied as |x|=|y|=1 and |rhs|>1.
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