I would like to find the minimum $$m_N = \min_{0\leq x\leq 2\pi} \{ f_N(x) \} \quad \hbox{ with } \quad f_N(x)=\frac{N}{2}+\sum_{k=1}^{N-1} (N-k) \cos(k x)$$ for all integers $N\geq 2$. It looks like it should be $m_N=0$ for all $N$ but I'm not able to prove it. Can you help me at least with some insight on how to address this problem? Thank you
2026-04-03 05:17:30.1775193450
Minimum of a finite Fourier sum
46 Views Asked by Bumbble Comm https://math.techqa.club/user/bumbble-comm/detail AtRelated Questions in SUMMATION
- Computing:$\sum_{n=0}^\infty\frac{3^n}{n!(n+3)}$
- Prove that $1+{1\over 1+{1\over 1+{1\over 1+{1\over 1+...}}}}=\sqrt{1+\sqrt{1+\sqrt{1+\sqrt{1+...}}}}$
- Fourier series. Find the sum $\sum_{n=1}^\infty \frac{(-1)^{n+1}}{2n+1}$
- Sigma (sum) Problem
- How to prove the inequality $\frac{1}{n}+\frac{1}{n+1}+\cdots+\frac{1}{2n-1}\geq \log (2)$?
- Double-exponential sum (maybe it telescopes?)
- Simplify $\prod_{k=1}^{l} \sum_{r=d}^m {{m}\choose{r}} \left(N-k \right)^{r} k^{m-r+1}$
- Sum of two martingales
- How can we prove that $e^{-jωn}$ converges at $0$ while n -> infinity?
- Interesting inequalities
Related Questions in FOURIER-SERIES
- order of zero of modular form from it's expansion at infinity
- Fourier series expansion of $\frac{\pi^4}{96}$ and $\frac{\pi^4}{90}$
- How is $\int_{-T_0/2}^{+T_0/2} \delta(t) \cos(n\omega_0 t)dt=1$ and $\int_{-T_0/2}^{+T_0/2} \delta(t) \sin(n\omega_0 t)=0$?
- Fourier series. Find the sum $\sum_{n=1}^\infty \frac{(-1)^{n+1}}{2n+1}$
- How get a good approximation of integrals involving the gamma function, exponentials and the fractional part?
- The convolution theorem for fourier series.:$ \widehat{f*g}(x) =2π\hat{g}(x)\cdot\hat{f}(x) $
- Ergodicity of a skew product
- Fourier Series on $L^1\left(\left[0,1\right)\right)\cap C\left(\left[0,1\right)\right)$
- Parseval's Identity Proof Monotone/Dominated Convergence Theorem
- How can I interchange the sum signs
Related Questions in MAXIMA-MINIMA
- optimization with strict inequality of variables
- Minimum value of a complex expression involving cube root of a unity
- Calculation of distance of a point from a curve
- Find all local maxima and minima of $x^2+y^2$ subject to the constraint $x^2+2y=6$. Does $x^2+y^2$ have a global max/min on the same constraint?
- Solving discrete recursion equations with min in the equation
- Trouble finding local extrema of a two variable function
- Why do I need boundedness for a a closed subset of $\mathbb{R}$ to have a maximum?
- Find the extreme points of the function $g(x):=(x^4-2x^2+2)^{1/2}, x∈[-0.5,2]$
- Maximizing triangle area problem
- Find the maximum volume of a cylinder
Related Questions in CONVOLUTION
- What is the result of $x(at) * δ(t-k)$
- Convolution sum
- PDF of the sum of two random variables integrates to >1
- If $u \in \mathscr{L}^1(\lambda^n), v\in \mathscr{L}^\infty (\lambda^n)$, then $u \star v$ is bounded and continuous.
- Proof of Young's inequality $\Vert u \star v \Vert_p \le \Vert u \Vert_1 \Vert v \Vert_p.$
- Duhamel's principle for heat equation.
- Computing the convolution of $f(x)=\gamma1_{(\alpha,\alpha+\beta)}(x)$
- Convolution of distributions property
- Self-convolution of $f(\vec{r}) = e^{-x^2-y^2}/r^2$
- Inverse $z$-transform similar to convolution
Related Questions in ROOTS-OF-UNITY
- On multiplicative and additive properties of cyclotomic polynomials
- Roots of $z^3 + 3iz^2 + 3z + i = 0$?
- Compute the determinant.
- Polygon discriminant sequence
- Is $\sqrt[6]{3} \in \mathbb{Q}(\sqrt[8]{21})$ and/or $\sqrt[4]{5} \in \mathbb{Q}(e^{\frac{2 \pi i}{25}})$?
- How to prove the following identity using complex numbers?
- Why does $\sqrt[4]{-2}=\frac{1+i}{\sqrt[4]{2}}$?
- Square root of a root of unity.
- Rational Trig Solutions for $n\ge 3$
- Solving simultaneous equations using de Moivre's Theorem and Roots of Unity
Trending Questions
- Induction on the number of equations
- How to convince a math teacher of this simple and obvious fact?
- Find $E[XY|Y+Z=1 ]$
- Refuting the Anti-Cantor Cranks
- What are imaginary numbers?
- Determine the adjoint of $\tilde Q(x)$ for $\tilde Q(x)u:=(Qu)(x)$ where $Q:U→L^2(Ω,ℝ^d$ is a Hilbert-Schmidt operator and $U$ is a Hilbert space
- Why does this innovative method of subtraction from a third grader always work?
- How do we know that the number $1$ is not equal to the number $-1$?
- What are the Implications of having VΩ as a model for a theory?
- Defining a Galois Field based on primitive element versus polynomial?
- Can't find the relationship between two columns of numbers. Please Help
- Is computer science a branch of mathematics?
- Is there a bijection of $\mathbb{R}^n$ with itself such that the forward map is connected but the inverse is not?
- Identification of a quadrilateral as a trapezoid, rectangle, or square
- Generator of inertia group in function field extension
Popular # Hahtags
second-order-logic
numerical-methods
puzzle
logic
probability
number-theory
winding-number
real-analysis
integration
calculus
complex-analysis
sequences-and-series
proof-writing
set-theory
functions
homotopy-theory
elementary-number-theory
ordinary-differential-equations
circles
derivatives
game-theory
definite-integrals
elementary-set-theory
limits
multivariable-calculus
geometry
algebraic-number-theory
proof-verification
partial-derivative
algebra-precalculus
Popular Questions
- What is the integral of 1/x?
- How many squares actually ARE in this picture? Is this a trick question with no right answer?
- Is a matrix multiplied with its transpose something special?
- What is the difference between independent and mutually exclusive events?
- Visually stunning math concepts which are easy to explain
- taylor series of $\ln(1+x)$?
- How to tell if a set of vectors spans a space?
- Calculus question taking derivative to find horizontal tangent line
- How to determine if a function is one-to-one?
- Determine if vectors are linearly independent
- What does it mean to have a determinant equal to zero?
- Is this Batman equation for real?
- How to find perpendicular vector to another vector?
- How to find mean and median from histogram
- How many sides does a circle have?