Lotto
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- Homework Statement
- Does series ##\sum_{n=1}^{\infty} \frac{\sin\left(\frac{n^2}{n+\frac 15}x\right)}{n^{x^2-3x+3}}## converges uniformly on the interval ##[0,2\pi]##?
- Relevant Equations
- ##\exists \epsilon >0 \, \forall n_0 \, \exists n \geq n_0 \, \exists p \, \exists x \in M: \left|\sum_{k=n+1}^{n+p} f_k(x)\right| \geq \epsilon##
First, I tried to show that ##f_n## converges uniformly on ##[0,2\pi]##, which is true since ##f_n \rightarrow 0## for ##n \rightarrow \infty## and ##\sigma_n=\mathrm{sup}\left| \frac{\sin\left(\frac{n^2}{n+\frac 15}x\right)}{n^{x^2-3x+3}} \right| \leq \frac{1}{|n^{x^2-3x+3}|} \leq \frac{1}{n^{\frac 34}}\rightarrow 0##. I can't use neither Leibnitz's test nor Abel's test. For Dirichlet's test I would need to show, that ##\sin\left(\frac{n^2}{n+\frac 15}x \right)## has partialy bounded sums on ##[0,2\pi]##, which I think is not true. Weierstrass M-test doesn't obviously work.
So I tried to prove that ##\exists \epsilon >0 \, \forall n_0 \, \exists n \geq n_0 \, \exists p \, \exists x \in [0,2\pi]: \left|\sum_{k=n+1}^{n+p} f_k(x)\right| \geq \epsilon ##, because that would mean that my series doesn't converge uniformly. I tried to choose ##n=n_0##, ##p=n_0## and ##x=\frac{1}{n^2_0}##, but that didn't work.
Don't you have any tips how to solve this problem?
So I tried to prove that ##\exists \epsilon >0 \, \forall n_0 \, \exists n \geq n_0 \, \exists p \, \exists x \in [0,2\pi]: \left|\sum_{k=n+1}^{n+p} f_k(x)\right| \geq \epsilon ##, because that would mean that my series doesn't converge uniformly. I tried to choose ##n=n_0##, ##p=n_0## and ##x=\frac{1}{n^2_0}##, but that didn't work.
Don't you have any tips how to solve this problem?
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