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Use the binomial series to expand the function as a power series. 3 (6 + x)3 Σ(1 ) 00 n=0 State the radius of convergence, R.

User Kkopczak
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1 Answer

5 votes

The radius of convergence
\(R\) for the original series
\((3)/((6+x)^3)\) is
\(6\).

The power series expansion of the function
\((3)/((6+x)^3)\) up to six terms is given by:


\[(1)/(72) - (x)/(144) + (x^2)/(432) - (5x^3)/(7776) + (5x^4)/(31104) - (7x^5)/(186624) + \cdots\]

Now, let's find the radius of convergence
\(R\) for this series.

The general term of the binomial series
\((1)/((1-x)^n)\) is given by
\(\binom{n+k-1}{k}x^k\), where
\(\binom{n}{k}\) is the binomial coefficient. In our case, for
\((3)/((6+x)^3)\), we can rewrite the function as
\((3)/(6^3) \cdot (1)/((1+(x)/(6))^3)\) and apply the binomial series expansion with
\(n=3\) and
\(a=(1)/(6)\).

The radius of convergence of the binomial series
\((1)/((1-x)^n)\) is 1, so for our transformed series, the radius of convergence will be
\(|a| \cdot R = (1)/(6) \cdot 1 = (1)/(6)\).

Therefore, the answer is
\(6\).

The complete question is here:

Use the binomial series to expand the function as a power series.


$$\begin{aligned}& (3)/((6+x)^3) \\& \sum_(n=0)^(\infty)(\perp)\end{aligned}$$(______)

State the radius of convergence,
$R$.

User Dan Iveson
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9.0k points