# Continuity at a point problem

1. Apr 7, 2012

### ferret93

I'm working on a problem as part of exam revision, but i've run into a bit of trouble so far. The problem is;
Give an (ε,δ) proof that f(x) = 1/$\sqrt{10 - x^2}$ is continuous at x = -1

The attempt at a solution
So far what i've gotten is f(x) - f(-1) = 1/($\sqrt{10 - x^2}$) - 1/3
= (3 - ($\sqrt{10 - x^2}$))/(3$\sqrt{10 - x^2}$)
= ((x^2) - 1)/(3$\sqrt{10 - x^2}$)

Then from here i've gotten -2 < x < 0 → 10 - x^2 > 6
i'm lost from where to go from here though i just can't see a way though, any help will be greatly appreciated.

Last edited: Apr 7, 2012
2. Apr 8, 2012

### tiny-tim

welcome to pf!

hi ferret93! welcome to pf!
the standard trick is to write that as (x+1) times the rest …

you use ε,δ to minimise (x+1), and some other limit to kepp the rest bounded