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I am being dumb! Math question!

TopiaTopia Registered User regular
edited October 2008 in Help / Advice Forum
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

  • EriosErios 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
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  • TopiaTopia 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
  • GameHatGameHat Registered User regular
    edited October 2008
    Here's a hint:

    L'hopital's Rule

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

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  • TopiaTopia Registered User regular
    edited October 2008
    physi_marc wrote: »
    If you haven't seen L'Hôpital'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'Hôpital's rule hasn't come up yet.

    Topia on
  • GameHatGameHat Registered User regular
    edited October 2008
    Topia wrote: »
    physi_marc wrote: »
    If you haven't seen L'Hôpital'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'Hôpital'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.

    otherwise factoring the bottom won't help you.

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

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

    Topia on
  • EriosErios Registered User regular
    edited October 2008
    Topia wrote: »
    physi_marc wrote: »
    If you haven't seen L'Hôpital'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'Hôpital's rule hasn't come up yet.

    It is probably the greatest thing.

    Erios on
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  • TopiaTopia Registered User regular
    edited October 2008
    ilmmad wrote: »
    Yeah did you learn the rules of differentiation yet?

    Yea, we're past differentiation and integration, but our teacher wants us to do certain questions certain ways... even if there is an easier way to do it. I find the derivatives, chain rule, all that way easier than basic algebra, strangely, but I am not allowed to use differentiation to find these answers on the test.

    He gives us an idea of whats on the test (6 limit questions, 4 differentiations, ect) and tells us that we have to do this for these questions, all that jazz. It's irritating.

    Edit: L'Hôpital's rule seems pretty easy, we probably went over it, but the prof probably didn't call it that.

    Topia on
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