Delta-Epsilon proof

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• November 25th 2008, 09:52 AM
fhernandezx3fh
Delta-Epsilon proof
I am having a real tough time with these proofs.

f(x)=2-(1/x)

find delta such that 0<|x-1|<d then |f(x)-1|<0.1

I understand what it means, but I'm having a hard time proving it.

I start out by working the epsilon inequality...

I end up with something like this...
|1/x||x-1|<0.1

Now I'm stuck. But from what I've been reading you would set
|x-1|<1

This is obviously not a good option given 1/x. So I chose 1/2.
I eventually get...
1/2<x<3/2

Now I don't understand the next step. This should be so easy.
• November 25th 2008, 11:26 AM
Plato
Let $\delta = .05$ and $\left| {x - 1} \right| < \delta < \frac{1}{2}$.
From what you have already done this means that $\frac{1}{x} < 2$.
Thus $\left| {1 - \frac{1}
{x}} \right| = \left| {\frac{{x - 1}}
{x}} \right| < 2\left| {x - 1} \right| < 2\left( \delta \right) = 0.1$