Expanding Cube Roots: Solving Limits with Maclaurin Series

  • Context: Graduate 
  • Thread starter Thread starter snoopies622
  • Start date Start date
  • Tags Tags
    Cube Expanding Root
Join the discussion
Ask a follow-up here, or get your own question answered by working scientists, mathematicians and engineers — people, not an autocomplete.
Real named experts · corrections over time · the nuance an AI answer skips
2 replies · 3K views
snoopies622
Messages
852
Reaction score
29
A quiz at the end of Steven Krantz's Calculus Demystified includes the following problem:
Find
[tex] \lim_{x \to \infty} [ \sqrt[3]{x+1}<br /> -<br /> \sqrt[3]{x} ][/tex]
I see how one can use the Maclaurin series to get
[tex] \sqrt[3]{x+1} = 1 + \frac {x}{3} - \frac {x^2}{9} + \frac {5 x^3}{81} + . . .[/tex]
but trying it with the cube root of x gives me zero plus an endless series of undefined terms.
Is there a way to expand [itex]\sqrt[3]{x}[/itex] and solve this problem?
 
Physics news on Phys.org
But why do you want expand that in series?
Isn't it by simple high school algebra :
ac{2}{3}&plus;%20%28x&plus;1%29^\frac{2}{3}&plus;x^{\frac{1}{3}}%28x&plus;1%29^{\frac{1}{3}}%20}.gif

for x>0?
 
Oh yeah, you're right zoki85 - thanks!

I also just realized that I could simply define y = x + 1, plug in y-1 for all the x's in the series above and there's the answer to my other question. :)