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Homework Help: Power series expansions - which is imossible

  1. Apr 28, 2009 #1
    Which of the following expansions is impossible?

    a [tex]\sqrt{x-1}[/tex] in powers of x

    b [tex]\sqrt{x+1}[/tex] in powers of x

    c [tex]ln(x)[/tex] in powers of (x-1)

    d [tex]tanx[/tex] in powers of (x-\pi / 4 )

    e [tex]ln(1-x)[/tex] in powers of x

    What are htey asking and how do i do this? the answer is A by the way
  2. jcsd
  3. Apr 28, 2009 #2


    Staff: Mentor

    Re: Expansions

    "In powers of (x - a)" means that x will be close to a, and that the function and its derivatives will be evaluated at a. Which of the functions above are defined at a (which will be 0, or 1, or pi/4 in these problems)?
  4. Apr 28, 2009 #3
    Re: Expansions

    So for a, x=0, and that is an imaginary result. Is this the same thing as saying it is centered around a?

    Thank you.
  5. Apr 29, 2009 #4


    Staff: Mentor

    Re: Expansions

    If a = 0, it is.
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