Tuesday, 28 January 2014

radicals - Square root inequality revisited

This is a follow-up question of this one:
Proof of the square root inequality 2n+12n<1n<2n2n1



I am interested in the following generalizations of the square root inequality.
Let ε,δ>0. Then
ε+δε<δ2ε.



If additionally δ<ε, then
δ2ε<εεδ.
The proof is similar as answered in my previous question.



Moreover, if ε,δC are any complex numbers and is a complex root, then
min(|ε+δε|,|ε+δ+ε|)min(|δ||ε|,|δ|).


I have trouble to prove this one, but it should hold (it is not from me). What I have yet is the following: first suppose
|ε+δε||ε+δ+ε|.

Then
|ε+δε|2|δ|,

so that

|ε+δε||δ|.

Similarly, when
|ε+δε||ε+δ+ε|,

then
|ε+δ+ε||δ|,

so that
min(|ε+δε|,|ε+δ+ε|)|δ|.

Moreover,
|ε+δε|=|δ||ε+δ+ε|

and I don't know how to continue. Any help for solving this?

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