Find a power series for the function, centered at c, and determine the interval

Maiclubk

Maiclubk

Answered question

2021-11-03

Find a power series for the function, centered at c, and determine the interval of convergence. 
g(x)=32x-1,c=2

Answer & Explanation

unessodopunsep

unessodopunsep

Skilled2021-11-04Added 105 answers

 Geometric Power Series Centered at c: The geometric power series centered at c is a series of the form
a1(rc)=n=0a(rc)n,|rc|<1
where a is the first term and r-c is the common ratio.
The function is given by
f(x)=32x1,c=2
Writing f(x) in the form a1r produces
32x1=32(x2)+3
=33(1+23(x2))
=1(1+23(x2))=a1r
which implies that a=1 and r=23(x2).
So, the power series for f(x) is
32x1=n=0arn
=n=0[23(x2)]n
=n=0(23)n(x2)n
=123(x2)+49(x2)2827(x2)3+
When the power series converges,
23|x2|<1|x2|<32
32<x2<32
12<x<312
This suggests that the convergence interval is (12,312)
Whenever the power series converges
23|x2|<1|x2|<32
32<x2<32
232<x<2+32
 

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