009C Sample Final 2, Problem 7

(a) Consider the function  $f(x)={\bigg (}1-{\frac {1}{2}}x{\bigg )}^{-2}.$  Find the first three terms of its Binomial Series.

(b) Find its radius of convergence.

Foundations:

Solution:

(a)

Step 1:

Step 2:

(b)

Step 1:
The Maclaurin series of  ${\frac {1}{(1-x)^{2}}}$  is
$\sum _{n=0}^{\infty }(n+1)x^{n}.$
So, the Maclaurin series of  ${\frac {1}{(1-{\frac {1}{2}}x)^{2}}}$  is
$\sum _{n=0}^{\infty }(n+1){\bigg (}{\frac {1}{2}}x{\bigg )}^{n}=\sum _{n=0}^{\infty }{\frac {(n+1)x^{n}}{2^{n}}}.$

Step 2:

Final Answer:
(a)
(b)

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