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Homework Help: Limitation first principle method

  1. May 28, 2012 #1
    1. The problem statement, all variables and given/known data
    Should be a simple question but its really tough for me because my lecturer had never teach me before about x^3

    Anyway, the question is find the first derivative by using first principle method :
    c) x^3+2x^2+1

    2. Relevant equations

    3. The attempt at a solution
    I did dy/dx = lim h->0 but during the process I am stuck because I am pretty confused about the expand part especially during the power for 3
  2. jcsd
  3. May 28, 2012 #2
    What do you mean by expanding for power 3? Assuming you want to expand (x+h)3, you need to multiply (x+h) thrice :wink: Or you can remember the result directly, or you can use the binomial theorem....

    Edit : Do show your work, it'll be easier to help you out then :smile:
    Last edited: May 28, 2012
  4. May 28, 2012 #3
    Yea, I meant by expanding the (x+h)3. I had managed to solve it using binomial theorem and it has saved me a lot of trouble. Thanks a lot Infinitum. Cheers :)
  5. May 28, 2012 #4
    You're welcome! :smile:

    On a side note,
    (a+b)3 is quite a commonly used identity, just like (a+b)2. It will surely help to memorize it.
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