Questions tagged [maxima-minima]

In mathematical analysis, the maxima and minima (the respective plurals of maximum and minimum) of a function, known collectively as extrema (the plural of extremum), are the largest and smallest value of the function, either within a given range (the local or relative extrema) or on the entire domain of a function (the global or absolute extrema).

In mathematical analysis, the maxima and minima (the respective plurals of maximum and minimum) of a function, known collectively as extrema (the plural of extremum), are the largest and smallest value of the function, either within a given range (the local or relative extrema) or on the entire domain of a function (the global or absolute extrema).

As defined in set theory, the maximum and minimum of a set are the greatest and least elements in the set, respectively. Unbounded infinite sets, such as the set of real numbers, have no minimum or maximum.

A real-valued function $f$ defined on a domain $X$ has a global (or absolute) maximum point at $x^∗$ if $f(x^∗) \ge f(x)$ for all $x$ in $X$. Similarly, the function has a global (or absolute) minimum point at $x^∗$ if $f(x^∗) \le f(x)$ for all $x$ in $X$. The value of the function at a maximum point is called the maximum value of the function and the value of the function at a minimum point is called the minimum value of the function.

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A very general method for proving inequalities. Too good to be true?

Update I 'repaired' this method, but it changed a lot and I have some different questions, so I posted it separately here. As training for the olympiad, I have to solve a lot of inequalities. Recently, I found a very general method to solve…
Mastrem
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Finding the largest equilateral triangle inside a given triangle

My wife came up with the following problem while we were making some decorations for our baby: given a triangle, what is the largest equilateral triangle that can be inscribed in it? (In other words: given a triangular piece of cardboard, what is…
ShreevatsaR
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Prove that $(1+x)^\frac{1}{x}+(1+\frac{1}{x})^x \leq 4$

Prove that $f(x)=(1+x)^\frac{1}{x}+(1+\frac{1}{x})^x \leq 4$ for all $x>0.$ We have $f(x)=f(\frac{1}{x}), f'(x)=-\frac{1}{x^2}f'(\frac{1}{x}),$ so we only need to prove $f'(x)>0$ for $0 < x < 1.$
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Show that the maximum value of this nested radical is $\phi-1$

I was experimenting on Desmos (as usual), in particular infinite recursions and series. Here is one that was of interest: What is the maximum value of $$F_\infty=\sqrt{\frac{x}{x+\sqrt{\dfrac{x^2}{x-\sqrt{\dfrac{x^3}{x+ \sqrt{…
TheSimpliFire
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What are the common abbreviation for minimum in equations?

I'm searching for some symbol representing minimum that is commonly used in math equations.
Darqer
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Determine the maximum of $f(x) = x + \sqrt{4-x^2}$ without calculus

I was given this problem in a Calc BC course while we were still doing review, so using derivatives or any sort of calculus was generally forbidden. We were only doing review because a lot of people hadn't taken Calc AB due to scheduling issues so…
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Maximum area of a square in a triangle

I want to calculate the area of the largest square which can be inscribed in a triangle of sides $a, b, c$ . The "square" which I will refer to, from now on, has all its four vertices on the sides of the triangle, and of course is completely…
Sawarnik
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How to prove $e^x\left|\int_x^{x+1}\sin(e^t) \,\mathrm d t\right|\le 1.4$?

Related question asked by me on MathOverflow: How to prove $e^x\left|\int_x^{x+1}\sin(e^t) \,\mathrm d t\right|\le 1.4$? This is a follow-up question to the question How to prove $ \mathrm{e}^x\left|\int_x^{x+1}\sin\mathrm e^t \mathrm d…
Maximilian Janisch
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Does a polynomial that's bounded below have a global minimum?

Must a polynomial function $f \in \mathbb{R}[x_1, \ldots, x_n]$ that's lower bounded by some $\lambda \in \mathbb{R}$ have a global minimum over $\mathbb{R}^n$?
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Investigate maxima of Gaussian integral over sphere.

Let $\alpha>0$ be a positive parameter and consider the function $$f(x) = \int_{\mathbb S^{n-1}} e^{-\alpha \left\lVert x-y \right\rVert^2} dS(y)$$ for $x \in \mathbb R^n.$ So, since this was asked, although we integrate over the unit sphere, the…
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Finding the maximum value without using derivatives

Find the maximum value of $$f(x)=2\sqrt{x}-\sqrt{x+1}-\sqrt{x-1}$$ without using derivatives. The domain of $f(x)$ is $x \in [1,\infty)$. Then, using derivatives, I can prove that the function decreases for all $x$ from $D(f)$ and the maximum…
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Is the minimum of this functional $C^{\infty}$?

The problem: Let us define $$ \mathscr{F}(u)=\int_0^1(u'(x))^4-e^x\sin (u(x))\, \mathrm{d}x $$ for $u \in W^{1,1}([0,1])$ such that $u(0)=A$ and $u(1)=B$. It don't matters what $A$ or $B$ are, because I am interested in the reasoning. I am asked to…
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Are these continued fractions of integrals known?

Motivated by this paper on polynomial continued fractions (Bowman, 2000), I thought about various extensions to current definitions of these fractions. What if we defined a continued fraction such that the numerator of each fraction is the integral…
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Maximum value of a function. I am not able to check double derivative.

Can someone explain me how $\sin^p x \cos^q x$ attains maximum at $\tan^2 x = \frac pq$. I am not able to check whether double derivative is positive or negative. Question Show that $$\sin^p\theta\cos^q\theta$$ attains a maximum when…
HoLyDeViL
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A very general method for solving inequalities repaired

Yesterday, I asked a question about a very general method for solving equations I had found here. As it turned out, there were quite some problems with my method and I got a lot of good feedback. After thinking about it for a while, I've come up…
Mastrem
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