Power series and uniform convergence.

In summary, to determine the uniform convergence of the given power series on the interval [-1/3, 1/3], we can use the Weierstrass M-test. By choosing a suitable sequence of positive real numbers and using the ratio test, we can show that the series is uniformly convergent on this interval.
  • #1
MissC
1
0
Hi.
I have this power serie (2^n/n)*z^n that runs from n=1 to infinity, and I have to show whether it's uniform konvergence on [-1/3, 1/3] or not.

I hope someone can help me with this.
 
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  • #2
It is fairly standard to use the "ratio test" or "root test" to determine convergence of a power series. And I presume you know that "if a power series converges on a closed and bounded interval, then it converges uniformly there."
 
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  • #3


Hi there,

To determine whether the given power series is uniformly convergent on the interval [-1/3, 1/3], we can use the Weierstrass M-test. This test states that if we can find a sequence of positive real numbers {M_n} such that the series of M_n converges, and for all n, |f_n(x)| < M_n for all x in the interval of interest, then the series of f_n(x) is uniformly convergent on that interval.

In this case, we can let M_n = (2^n/n)*(1/3)^n. We can see that the series of M_n converges using the ratio test. And for all x in [-1/3, 1/3], we have |f_n(x)| = |(2^n/n)*x^n| <= (2^n/n)*(1/3)^n = M_n. Therefore, the given series is uniformly convergent on the interval [-1/3, 1/3].

Hope this helps!
 

FAQ: Power series and uniform convergence.

What is a power series?

A power series is a series of the form ∑n=0∞ an(x-c)n, where an are constants and c is a fixed value. It is a type of infinite series that represents a function as an infinite sum of powers of x.

What is uniform convergence?

Uniform convergence is a type of convergence in which the rate of convergence is independent of the choice of the point in the domain. In other words, as the number of terms in the series approaches infinity, the difference between the partial sum and the actual value of the function becomes smaller and smaller at the same rate for all points in the domain.

How do you determine if a power series is uniformly convergent?

A power series is uniformly convergent if the sequence of partial sums converges uniformly to the function on some interval. This can be determined by using the Weierstrass M-test or the Cauchy criterion for uniform convergence.

What is the radius of convergence for a power series?

The radius of convergence for a power series is the distance from the center of the series at which the series converges. It can be calculated using the ratio test or the root test, and it represents the interval of x values for which the power series converges.

How can power series be used to represent functions?

Power series can be used to represent functions by expanding the function into a series of powers of x. This can be a useful tool in calculus for evaluating functions, approximating functions, and solving differential equations. Additionally, many common functions such as trigonometric functions, logarithmic functions, and exponential functions can be represented as power series.

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