MacLaurin Series for f(x)=ln|1+x^3|

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SUMMARY

The MacLaurin series representation for the function f(x) = ln|1+x^3| can be derived using Taylor series expansion at x=0. Initial derivatives at x=0 yield f(0) = 0, f'(0) = 0, f''(0) = 0, and f'''(0) = 6, leading to a pattern in the coefficients of the series. The series appears to follow the formula (-1)^(n-1)*3*(n-1)!, with n starting at 0, indicating a complex relationship between the derivatives and the series terms. The radius of convergence can be determined using the ratio test, and further exploration is needed to approximate the integral of ln|1+x^3| from 0 to 2 using this series.

PREREQUISITES
  • Understanding of MacLaurin series and Taylor series expansions.
  • Familiarity with derivatives and their computation.
  • Knowledge of geometric series and their applications.
  • Experience with the ratio test for determining convergence.
NEXT STEPS
  • Study the derivation of the MacLaurin series for ln(1+t) and apply it to ln(1+x^3).
  • Learn how to compute higher-order derivatives effectively for series expansion.
  • Research the ratio test for convergence and its application in series analysis.
  • Explore numerical methods for approximating integrals using series representations.
USEFUL FOR

Students and educators in calculus, particularly those focusing on series expansions, derivatives, and integral approximations. This discussion is beneficial for anyone seeking to deepen their understanding of MacLaurin series and their applications in mathematical analysis.

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Homework Statement


Find the MacLaurin series representation for f(x)=ln|1+x^3|

Homework Equations


1/(1-x) = \sumx^n = 1+x+x^2+x^3+... |x|<1

The Attempt at a Solution


right.
so maclaurin series by default means it expands as a taylor series where x=0
f(0)= ln|1+x^3| = 0
f'(0)= 3(0)^2/(1+0^3)^1 = 0/1 = 0
f''(0)= -3(0)^2/(1+0^3)^2 = -0/1 = 0
f'''(0)= 6(0)^6-42(0)^3+6/(1+0^3)^3 = 6
so on and so forth

it's taken me a few hours but so far, i can't seem to use that relevant equation to find the maclaurin series.

i may have gotten kinda close, b/c I've found so far that
fn(0)=(very complex numerator that kind of looks like a quadratic or polynomial formula with switching signs)/(1+x3)n

i've done upto 9th derivative(and further more) and found that this goes something like:
0,0,0,6,0,0,-360,0,0,120960,0,0,-119750400,0,0,261534973600
and that the series the pretty much follows (-1)^(n-1)*3*(n-1)!, where n starts at 0, with 2 blanks in between.

i know I'm missing something, and this isn't that hard.
please help.

--
then I'm supposed to find radius of convergence, which i think i can probably get using by ratio test..
then need to find out how many terms are needed to appx it within 0.0001...
then find out why appx'ing integral of ln|1+x^3| from 0 to 2 by using the series representation is wrong.
but i think i can figure those out once the first part is done.
 
Last edited:
Physics news on Phys.org
Find the Maclaurin series for the derivative of ln(1+x^3), by using the geometric series.
 
Or find the Maclaurin series for ln(1+t) and then let t=x^3.
 

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