Power series: Why is this power series equal to log(2)?

In summary, the conversation discusses the series ##\sum_{n=0}^\infty (-1)^n \frac {x^\left(n+1\right)}{n+1}## where x=1 and how it can be evaluated using the Leibniz test and integration. The result of the series is found to be equal to ##log(2)## by plugging in the value of x.
  • #1
DottZakapa
239
17
Homework Statement
##\sum_{n=0}^\infty (-1)^n \frac {x^\left(n+1\right)}{n+1}## for x=1
Relevant Equations
power series
##\sum_{n=0}^\infty (-1)^n \frac {x^\left(n+1\right)}{n+1}## for x=1

##\sum_{n=0}^\infty (-1)^n \frac {1^\left(n+1\right)}{n+1}##

i've tried leibniz test but i can only find that it converges

why is this power equal to ##log(2)##?

i've also tried with ##\sum_{n=0}^\infty\log \left (1+\frac 1 {n+1}\right)##

but does not lead to that result

what am i missing ?
 
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  • #2
Hint: Try integrating the series for ##\frac{1}{1+x}##.
 
  • #3
vela said:
Hint: Try integrating the series for ##\frac{1}{1+x}##.

which is log(1+x)
:doh:
ok, didn't understood that if it converges i could plug there the value of x to see at which value converges. Thank you. :smile:
 

1. What is a power series?

A power series is a series of the form ∑n=0^∞ cn(x-a)n, where a is a constant and cn are coefficients. It is a mathematical representation of a function, where the value of the function at any point x is given by the sum of the series.

2. How is a power series related to logarithms?

A power series can be used to represent logarithmic functions. In particular, the power series for log(x) is given by ∑n=1^∞ (-1)n+1(x-1)n/n. This series only converges for values of x between 0 and 2, and when x=2, it converges to log(2).

3. Why is the power series for log(2) equal to log(2)?

The power series for log(x) was derived using the Maclaurin series expansion. When x=2, the series converges to log(2) because the Maclaurin series for log(x) only converges for values between 0 and 2.

4. Can any other value be represented by the power series for log(2)?

No, the power series for log(x) only converges for values between 0 and 2. When x is outside of this range, the series does not converge and therefore cannot represent any other value.

5. How accurate is the power series representation of log(2)?

The accuracy of the power series representation of log(2) depends on the number of terms used in the series. The more terms used, the closer the approximation will be to the exact value of log(2). However, the series will never give an exact value as it is an infinite series.

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