1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Fill in the blank help

  1. May 8, 2006 #1
    These two problems are a big pain (never worked a problem in this format before). # represents a number that needs to be plugged into the problem to equal the given number. All #'s are the same when you find them so in problem 1 the 4 unknown #s are not different. #=#

    # + 4*#^2+9*#^3+16*#^4.... =6

    i re wrote it so it looks like this # +2^2 * #^2 + 3^2 * #^3 = 4^2 * #^4
    Looks like a taylor series. Series of 1 over 1-x? but how do i apply that?

    lim (1+#x)^#/x = 4

    for 2 i was really confused. I was thinking of appyling the natrual log so i would get ln #/x (1+#x) and apply L'Hopital's rule to that but i dont think thats the correct method.

    Sorry im just really confused because I never worked problems like these (fill in the blank) before. Any help would be apperciated.
  2. jcsd
  3. May 8, 2006 #2


    User Avatar
    Science Advisor
    Homework Helper

    HINT: If

    [tex]f(x) = \frac {1}{1-x}[/tex]


    [tex]\frac {d}{dx} \left( x \frac {df}{dx} \right) = 1 + 2x + 9x^2 + \cdot \cdot \cdot [/tex]
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?