# I am being dumb! Math question!

Registered User regular
edited October 2008
Okay this is very very easy stuff so you smart folk shouldn't have a problem. I am studying for a calc test (yes studying so I'm not cheating) and have problems with just this one question so far.

Indicate limit:

lim ..... | x - a |
x->a- (x^2) - (a^2)

Now I know the answer is -(1/2a)

Help! This shouldn't be so hard, but I am having problems right now.

Topia on

## Posts

• Registered User regular
edited October 2008
is that as X approaches a or -a?

EDIT: it's been a while since calc, but I think you have to invoke L'Hopital's rule.

Erios on
Steam: erios23, Live: Coconut Flavor, Origin: erios2386.
• Registered User regular
edited October 2008
It's a-, so a from the left, or negative side of the x axis, I guess it means.

Edit: there is another question exactly the same that is a+, so a from the right, or positive side, too.

Topia on
• Registered User regular
edited October 2008
Here's a hint:

L'hopital's Rule

GameHat on
• Positron Tracker In a nutshellRegistered User regular
edited October 2008
If you haven't seen L'HÃ´pital's rule, you may try factoring the denominator and simplifying.

physi_marc on
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• Registered User regular
edited October 2008
physi_marc wrote: »
If you haven't seen L'HÃ´pital's rule, you may try factoring the denominator and simplifying.

I guess this is my answer. I tried but must have made a mistake somewhere along the way. L'HÃ´pital's rule hasn't come up yet.

Topia on
• Registered User regular
edited October 2008
Topia wrote: »
physi_marc wrote: »
If you haven't seen L'HÃ´pital's rule, you may try factoring the denominator and simplifying.

I guess this is my answer. I tried but must have made a mistake somewhere along the way. L'HÃ´pital's rule hasn't come up yet.

Just remember that if you are approaching a from the left, X<=a. So |X-a| will always be equal to a-x.

approaching a from the right, then X>=a. And |x-a| = x-a.

GameHat on
• Registered User regular
edited October 2008
Yeah did you learn the rules of differentiation yet?

• Registered User regular
edited October 2008
Awesome I got it. Shit, so damn easy haha. Thanks guys. Help me with my hurdles.

Topia on
• Registered User regular
edited October 2008
Topia wrote: »
physi_marc wrote: »
If you haven't seen L'HÃ´pital's rule, you may try factoring the denominator and simplifying.

I guess this is my answer. I tried but must have made a mistake somewhere along the way. L'HÃ´pital's rule hasn't come up yet.

It is probably the greatest thing.

Erios on
Steam: erios23, Live: Coconut Flavor, Origin: erios2386.
• Registered User regular
edited October 2008