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Real-valued functions of real variable, analytic properties of functions and sequences, limits, continuity, smoothness of these.

4 votes
1 answer
382 views

$\sum_{k=1}^n\frac{\sin kx}{k^\alpha} >0\quad\text{for all}\ n=1,2,3,\ldots\ \text{and}\ 0<x...

The Fejer-Jackson inequality as follows: $$\sum_{k=1}^n\frac{\sin kx}k>0\quad\text{for all}\ n=1,2,3,\ldots\ \text{and}\ 0<x<\pi.$$ I conjecture that the inequality as follows holds: $$\sum_{k=1}^n\f …
Đào Thanh Oai's user avatar
2 votes
1 answer
432 views

$\sum_{k=1}^n(-1)^k\frac{\sin kx}{k^{\alpha}} < 0 ?$ with $\alpha \ge 1$ and $n=1, 2,\cdots$

Could You give a poof, comment or reference for the inequality as follows: $$\sum_{k=1}^n(-1)^k\frac{\sin kx}{k^{\alpha}} < 0$$ for all $n=1,2,3,\ldots$ and $0<x<\pi$ and $\alpha \ge 1$ See also: …
Đào Thanh Oai's user avatar
0 votes
1 answer
190 views

Is $f(x)$ is more curvature than $g(x)$ then length of $f(x)$ seem longer than length of $g(...

In my obsevation: If $f(x)$ and $g(x)$ be two continuous funcions, and they have derivative and second derivative are also continuous in interval $[a, b]$. If $f(x)$ is more curvature than $g(x)$ in …
Đào Thanh Oai's user avatar
0 votes
2 answers
230 views

An inequality on length of two curves [closed]

I am looking for a proof, reference, comment of an inequality as follows: If $f(x)$ and $g(x)$ be two continuous derivative funcions in interval $[a, b]$. Such that: $f(a)=g(a)$ and $f( …
Đào Thanh Oai's user avatar
-3 votes
1 answer
387 views

A generalization of Chebyshev's sum inequality

From some my previous questions here and here and well-known rearrangement inequality. I pose an inequality as follows and I am looking for the proof or a reference. Inequality: Let $y=f …
Đào Thanh Oai's user avatar