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Limits question

  1. Aug 28, 2005 #1
    I just started calculus and we are doing limits. I was doing fine on my hmwrk until i came to this problem:

    Find lim f(x+∆x) – f(x)/ ∆x

    f(x)= x^2 – 4x

    I have no idea what the delta means... I know in chem it means "a change in", but I don't know what to do with it here. My book doesn't explain it either. Please help! Thanks
  2. jcsd
  3. Aug 28, 2005 #2
    delta x ->0
    means as x approaches zero

    or in other words the change in the value of x is getting so small that it is almost zero.
  4. Aug 28, 2005 #3
    oh so it changes nothing?
  5. Aug 28, 2005 #4
    or what am i supposed to do with the delta x value?
  6. Aug 28, 2005 #5


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    I seriously doubt that. For purposes of solving your problem and to get you accustomed to the concept why don't you just replace the [itex]\Delta x[/itex] with something more friendly looking like a? Then you can carry out your algebra and examine what happens when a is made arbitrarily small.
  7. Aug 28, 2005 #6
    Trust me. I have read the entire chapter looking for something explaining the delta and there is nothing. Thanks for the tip though.
  8. Aug 28, 2005 #7
    ok, so I worked out the problem and got 2x+a... is this correct? For some reason I dont think it is, but I thought I worked it out right...
  9. Aug 29, 2005 #8


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    You should have gotten [itex]2x - 4 + a[/itex]. Recheck your algebra.
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