Sum of Series $\approx$ Error Estimation

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SUMMARY

The discussion focuses on estimating the sum of the series $\sum_{n=1}^{\infty}\frac{1}{3^n+4^n}$ by calculating the first 10 terms and evaluating the error. It is established that for large values of $n$, the term $1/(3^n+4^n)$ approximates to $1/4^n$. The upper bound for the truncation error is determined using the integral $\int_{10}^{\infty} 1/4^x\; dx$, while the lower bound is given by the first neglected term, $1/(3^{11}+4^{11})$. This method provides a clear framework for error estimation in infinite series.

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use the sum of the first 10 terms to approximate the sum of the series. Estimate the error.

$\sum_{n=1}^{\infty}\frac{1}{3^n+4^n}$
 
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ineedhelpnow said:
use the sum of the first 10 terms to approximate the sum of the series. Estimate the error.

$\sum_{n=1}^{\infty}\frac{1}{3^n+4^n}$

I will leave you to sum the first ten terms, then we observe:

As $n$ becomes large $3^n \ll 4^n$ so $1/(3^n+4^4)\approx 1/4^n$ and $1/(3^n+4^4) < 1/4^n$ so the remainder after summing the first 10 terms of the series is approximately equal to (and less than) $\int_{10}^{\infty} 1/4^x\; dx$ ...

The above is an upper bound on the truncation error, in this case a lower bound is provided by the first neglected term: $1/(3^{11}+4^{11})$

.
 
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