What is the radius and interval of convergence for the given power series?

I must have divided wrong. In summary, the radius of convergence for the given series is 1 and the interval of convergence is -1/3 < x < 5/3.
  • #1
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Homework Statement



Find the radius of convergence and the interval of convergence of the series sigma[n=1,inf] ((3x-2)^n/(n^2*3^n))

Homework Equations


The Attempt at a Solution



sigma[n=1,inf] ((3x-2)^n/(n^2*3^n))
I applied the Root Test
p=lim n->inf |(3x-2)^n/(n^2*3^n)|^(1/n) = lim n->inf |(3x-2)/(3n^(2/n))| = 0
So the series Converges but I'm lost as to how to come up with the radius of convergence or the interval of convergence
 
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  • #2
My bad I did this completley wrong let me work it out some more
 
  • #3
p=lim n->inf |(3x-2)^n/(n^2*3^n)|^(1/n) = lim n->inf |(3x-2)/(3n^(2/n))| = |x-2/3|

sense for the root test 0<= p < 1
I have
0<= |x-2/3| <1
whose solution is
-1/3 < x < 5/3
which is my interval of convergence
So the radius of convergence is
(5/3-1/3)/2 = 2/3

does this look better?
 
  • #4
Looks okay except you made a small error calculating the radius of convergence. You should find it equal 1.
 
  • #5
Ah thanks
 

1. What is a power series in calculus?

A power series in calculus is an infinite series that represents a function as a sum of powers of x. It is used to approximate and analyze functions, and is often used in the study of limits, derivatives, and integrals.

2. How do you find the radius and interval of convergence of a power series?

To find the radius of convergence, you can use the ratio test by taking the limit as n approaches infinity of the absolute value of the (n+1)th term divided by the nth term. The radius of convergence is the value of x for which the limit is equal to 1. The interval of convergence can be determined by testing the endpoints of the interval of convergence and checking for convergence or divergence.

3. What is the difference between a power series and a Taylor series?

A power series is a representation of a function as a sum of powers of x, while a Taylor series is a special type of power series that represents a function as a sum of powers of x centered at a specific point. The coefficients in a Taylor series are determined by taking the derivatives of the function at the center point, while the coefficients in a power series can be any real number.

4. How can power series be used to approximate functions?

Power series can be used to approximate functions by truncating the series at a certain term and using the resulting polynomial as an approximation of the function. The more terms that are included in the series, the more accurate the approximation will be.

5. What is the Maclaurin series and how is it related to power series?

The Maclaurin series is a special type of Taylor series where the center is at x=0. It is used to approximate functions by using a power series representation centered at x=0. It is related to power series because it is a type of power series, but with a specific center point.

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