0
votes
1answer
43 views

How to obtain the number of real valued zeroes of a polynomial?

While I know there's no analytical formula for the roots of a general polynomial of degree five and higher, I wonder whether there is at least something like a parabola's discriminant to determine how ...
1
vote
0answers
28 views

Roots of this trigonometric polynomial

Let $f:[0,2\pi) \rightarrow \mathbb{R}$ with $f(x):=\sum_{n=0}^{k}a_n \left(1+\cos(x)\right)^n$ for arbitrary $a_n$ with $a_k \neq 0$. My question is: What is the maximum number of zeros that this ...
1
vote
1answer
72 views

Roots of $\tan x - x$

The function $\tan x - x$ has exactly one root $x_n$ in the interval $(n\pi, (n + \frac{1}{2})\pi)$. Show that $$x_n = n\pi + \frac{\pi}{2} - \frac{1}{n\pi} + r_n$$ where $\lim_{n\rightarrow \infty} n ...
1
vote
1answer
50 views

Kantorovich Theorem example

I need to write in C a program that finds roots of a 6th order polynomial. I was thinking of using Kantorovich Theorem convergence of Newton's method to find when can I use Newton-Rhapson method. I'm ...
12
votes
2answers
86 views

Function such that zeros$=$order of the derivative

Does there exist a function $f\in C^n(\mathbb{R},\mathbb{R})$ for $n\ge2$ such that $f^{(n)}$ has exactly $n$ zeros, $f^{(n-1)}$ has exactly $n-1$ zeros and so on ? Where $f^{(n)}$ is the nth ...
1
vote
2answers
33 views

Intermediate value theorem problem(proving only one root)

This problem is likely very trivial. Let $f(x) = x^5 - 5x + p$. Show that $f$ can have at most one root in $[0,1]$,regardless of the value of p. This seems to be an IVT problem, so I will go ...
3
votes
1answer
38 views

Is the set of continuous function with Lebesgue zero set a Borel set in continuous space?

Let $D$ be a domain in $\mathbb{R^d}$ and denote the continuous function space on $D$ as $X := C(\overline{D})$ where we can define the $\sigma$-algebra $\mathscr{B}(X)$ of $X$, that is sets in $X$ ...
16
votes
3answers
360 views

The function $f'+f'''$ has at least $3$ zeros on $[0,2\pi]$.

Show that if $f\in \mathcal{C}^3$ and $2\cdot\pi$ periodic then the function $f'+f'''$ has at least $3$ zeros on $[0,2\pi]$. My attempt : f is $2\pi$ periodic and $\mathcal{C}^3$, we have : ...
30
votes
4answers
871 views

$p_n(x)=p_{n-1}(x)+p_{n-1}^{\prime}(x)$, then all the roots of $p_k(x)$ are real

$p_0(x)=a_mx^m+a_{m-1}x^{m-1}+\dotsb+a_1x+a_0(a_m,\dotsc,a_1,a_0\in\Bbb R)$ is a polynomial, and $$p_n(x)=p_{n-1}(x)+p_{n-1}^{\prime}(x),\qquad n=1,2,\dotsc$$ then, there exist $N\in\Bbb N$, such ...
0
votes
2answers
55 views

Ideas on how to proceed with a proof?

Sorry if this is a nonspecific question - I can provide more details but at this point I need general ideas on a proof strategy. So I recently reduced a rather difficult optimization problem to ...
0
votes
0answers
15 views

Estimate error when using the result of an expanded equation

I would like to know how to deal with the error term in expanded expression. For example consider the function $\displaystyle f(x)=A\text e^{-(x+\lambda)^2}+B\text e^{-(x-2\lambda)^2}\;, $ where ...
1
vote
3answers
61 views

A polynomial's roots

Let $Q_n(x) = (x^2-1)^n$ and $P_n(x) = Q_n^{(n)}(x)$. Using Rolle's theorem, prove that $P_n$ has exactly $n$ roots.
2
votes
3answers
92 views

Numerical Solution of $\frac{x}{1-e^{-x}} -5 = 0$

I am working on a problem at the moment which cuts down to the following question: How do I get a numerical solution for: $$\frac{x}{1-e^{-x}} -5 = 0?$$ I've been thinking about using Newton's ...
0
votes
0answers
47 views

Finding roots and studying the sign if a polynomial?

We have two polynomials $g(x):= 1+x+\cdots+x^{2m+1}$ and $f(x):= 1+x+\frac{x²}{2}+\cdots+\frac{x^n}{n}$. For the first one, we wish to find the real roots and study the sign as $x$ varies. I ...
18
votes
2answers
666 views

Prove that there exists $n\in\mathbb{N}$ such that $f^{(n)}$ has at least n+1 zeros on $(-1,1)$

Let $f\in C^{\infty}(\mathbb{R},\mathbb{R})$ such that $f(x)=0$ on $\mathbb{R}$\ $(-1,1)$. Prove that there exists $n\in\mathbb{N}$ such that $f^{(n)}$ has at least n+1 zeros on $(-1,1)$ My attempt : ...
5
votes
1answer
98 views

Prove that a mapping $f:[-1,1]^2\to\mathbb R^2$ with certain properties has the value $(0,0)$.

The mapping $f:[-1,1]^2\to\mathbb R^2$ is known to be continuous. Also the image of the upper edge of the rectangle is contained in the upper half-plane, the left edge's image is contained in the left ...
1
vote
1answer
69 views

Find the root of the polynomial?

Consider the root of the polynomial $p(x) = x^n+a_{n-1}x^{n-1}+a_{n-2}x^{n-2}+\dots+a_1x -1$. Suppose that $p(x)$ has no roots in the open unit disc in a complex plane and $p(-1)=0$. Show that ...
0
votes
1answer
102 views

If f is n-times differentiable, and $f^n$ is never 0, then f has at most n zeros in R

Let $n \ge 0$, let $f:\mathbb{R} \rightarrow \mathbb{R}$ be n-times diff erentiable on $\mathbb{R}$, and assume that $f^{(n)}(x) \neq 0$ for all $x \in \mathbb{R}$. Show that $f$ has at most $n$ zeros ...
0
votes
1answer
126 views

Prove there are 3 real roots to this equation using Rolle's Theorem

I need to prove there are $3$ real solutions to $x^5 - 4x + 2 = 0$. I know $f(-2)$ is negative, $f(0)$ is positive, $f(1)$ is negative, $f(2)$ is positive so that by IVT there are at least $3$ roots. ...
2
votes
2answers
123 views

The polynomial $P(x)=x^4 -\sqrt{7} x^3 + 4x^2 - \sqrt{22} x+15$ has four different roots. Prove that not all zeros of polynomial $P(x)$ are real

This is from my real analysis class. I know how to show a function has exactly one root but im not sure how to go about this.
3
votes
3answers
3k views

Prove using Rolle's Theorem that an equation has exactly one real solution.

So the question is; Prove that the equation $x^7+x^5+x^3+1=0$ has exactly one real solution. You should use Rolle’s Theorem at some point in the proof. And I have, Since $f(x) = x^7+x^5+x^3+1$ ...
2
votes
0answers
65 views

For which $\alpha$ do the $\epsilon$-neighborhoods of $\{k\alpha \mod 1 \mid k = 1, \ldots , poly(1/\epsilon) \}$ cover $[0,1]$?

For which $\alpha$ do the $\epsilon$-neighborhoods of $\{k\alpha \mod 1 \mid k = 1, \ldots , poly(1/\epsilon) \}$ cover $[0,1]$? In this paper on quantum computing (last paragraph of page 25), Dorit ...
1
vote
4answers
237 views

Prove that the polynomial $x^6+x^4-5x^2+1$ has at least four real roots.

Prove that the polynomial $x^6+x^4-5x^2+1$ has at least four real roots. Talking analysis here, using the definition of continuity, intermediate value theorem, and extreme value theorem.
1
vote
1answer
45 views

At which parameter value $c>0$ do the number of solutions of $\log(1+x^2)=x^c$ change?

I'm looking at the functions $x\mapsto \log(1+x^2)$ and $x\mapsto x^c,\ c>0$ on the interval $\mathbb R^+_0$. I'm interested in the properties of $$\log(1+x^2)=x^c.$$ Graphically, for small $c$, ...
4
votes
1answer
92 views

Real root of a complex equation.

I was working on a problem from Gamelin; where I was required to find out zeros of $2z^5+6z^1-1$ , in the unit disk (in $\mathbb C$). I applied Rouché's theorem and find out zeros in the unit ...
4
votes
1answer
76 views

What's wrong with my conjecture?

I was doing math homework, and I formulated the following conjecture from one of the questions: If $f(x)$, $g(x)$ and $h(x)$ are continuous functions and the equations $f(x) = h(x)$ and $g(x) = h(x)$ ...
4
votes
1answer
83 views

Minimum difference of roots of a polynomial and its derivative

Let $P(x) = (x-x_1)(x-x_2)...(x-x_n)$ where all the n roots are real and distinct. Let $y_1,y_2,...,y_{n-1}$ be the roots of $P'$. Show that $\min_{i\neq j}|x_i-x_j|<\min_{i\neq j}|y_i-y_j|$. My ...
0
votes
2answers
101 views

Simplifying equation into Newton Raphson form

Given the equation $\displaystyle{\int_{-x}^x\exp({-t^2})dt}=-\ln(x)$: a. Simplify the integral using Gauss method with 3 points. b. Solve given equation by Newton Raphson iterative ...
0
votes
0answers
106 views

Zeros of a power series

Suppose we have a power series with (real or complex) coefficients $\sum_{n \geq 0} a_n x^n$ (that has nonzero radius of convergence). Can one say something about its zeros in terms of the ...
0
votes
2answers
51 views

Number of real roots of $2^x = 1-x^2$ for $x\in (0,1)$

How can I found no. of real roots of $2^x = 1-x^2$ in $x\in (0,1)$ I did not found a method by which i can draw graph of two curve in the interval $x\in (0,1)$ please help me , Thanks Sorry ...
2
votes
2answers
149 views

Prove that $f$ has finite number of roots

Let $f:[0,1]\to \mathbb{R}$ be a differentiable function. If there do not exist any $x\in[0,1]$ such that $f(x)=f'(x)=0$, prove that $f$ has only finite number of zeros in $[0,1]$. I'm not ...
2
votes
2answers
61 views

Finding Root of an Equation with Variables Dependent on Each other

Sorry for the title. I'm sure there is better terminology. I'd be interested to here what that terminology is haha. Here is my problem: ...
2
votes
2answers
117 views

Condition For No Existence Of Real Root

$2x^{4}+5ax^{3}-2bx^{2}+1=0$ has no real root in $(5,2014)$ Find the conditions for $a$ and $b$ I am suspicious of even the existence of its solution and at a loss.
1
vote
1answer
105 views

Assume that the set of values where $f^{(k)}≠0$ is finite

Let $f:ℝ→ℝ$ be a real analytic function. Let $f^{(k)}$ be the $k$th derivative of $f$. Assume that the set of values where $f^{(k)}≠0$ is finite, then what we can say about the function $f$.
1
vote
1answer
66 views

Prove that $D$ is bijective with the integers set $ℤ$

Let $f:ℝ→ℝ$ be a real analytic function. Assume that $f$ has infinitely many zeros. Let $D$ be the set of those zeros. Prove that $D$ is bijective with the integers set $ℤ$.
0
votes
0answers
36 views

Unicity of solutions in several dimensions

Let $h:ℝ^{r+1}→ℝ^{r+1}$ be a real function. If $r=0$ and $h$ is bijective then we know that the equation $h(x)=y$ has a unique solution. My question is: How about the case where $r>0$? I know that ...
4
votes
1answer
134 views

Mean values theorem and countable sets

The mean values theorem says that there exists a $c∈(u,v)$ such that $$f(v)-f(u)=f′(c)(v-u)$$ My question is: Assume that $u$ is a root of $f$, hence we obtain $$f(v)=f′(c)(v-u)$$ Assume that $f$ is a ...
1
vote
1answer
52 views

Pick out the case(s) which ensure that the polynomial $p(\cdot)$ has a root in the interval $[0, 1]$

Please help me to solve the problem below. Consider the polynomial $p(x) = a_0 + a_1x + a_2x^2+\dots+ a_nx^n$, with real coefficients. Pick out the case(s) which ensure that the polynomial ...
4
votes
1answer
580 views

How to solve an equation using Newton's method with and without backtracking?

Lets assume I have this equation: $$\log(e^x+e^{-x})=2x+5,\quad x \in (-50,50).$$ As always we have to pick a starting point to solve this by Newton's method, but how can i know for what initial ...
4
votes
1answer
202 views

Do the momentum conservation equations have a unique solution?

In high energy physics, one often encounters conservation of momentum and energy equations of the following form: $$\begin{array}{rcr} \sum_i (-1)^{\alpha_i}\sqrt{k_i^2 + m_i^2} = 0 \\ \sum_i ...
2
votes
2answers
294 views

Properties of solutions of the functional equation $f(kx) = kf(x)$

My problem is that I have a function: $f\colon\mathbb R\to\mathbb R$ with the property that $f(kx) = kf(x)$ for all $k,x \in\mathbb R$. a) I shall show that $f(0)=0$ b) If $f$ is not the ...
1
vote
2answers
426 views

find number of solution for given equation

suppose we we have following equations and conditions Let $k$ be the number of real solutions of the equation $e^x+x-2=0$ in the interval $[0, 1]$ and and let $n$ be the number of real solutions ...
2
votes
4answers
191 views

Proving all roots of a sequence of polynomials are real

Let the sequence of polyominoes $R_n(z)$ be defined as follows for $n\geqslant1$: $$R_n(z)\;= \;\sum_{r=0}^{\lfloor\frac{n-1}{2}\rfloor} \tbinom{n}{2r+1}(4z)^r.$$ I would like to prove that all the ...
4
votes
2answers
87 views

Number of times two rescaled, 'fully' monotonic functions can cross

Consider two functions $f: [0,1) \rightarrow \mathbb{R}$ and $g: [0,1) \rightarrow \mathbb{R}$. Suppose $f(x) > g(x)$ for all $x \in [0,1)$. Suppose further that $f$ and $g$ are infinitely ...
6
votes
1answer
119 views

Prove the equation has a root.

Assume that $f$ is a bounded and differentiable function in $(0,1)$. If $f({1\over 2})=0$, prove that the equation, $$2f(x)+xf'(x)=0,$$ has at least one root in $(0,{{1}\over{2}})$. I tried to do it ...
2
votes
1answer
107 views

The way to figure out whether the multi-variable polynomial has roots.

Let's have a multi-variable high degree polynomial $f(x_1, x_2, \dots, x_n)$. I am looking for efficient way to figure out if there are any roots in real numbers for: $0 \le x_1 \le 1\\ 0 \le x_2 ...
3
votes
3answers
165 views

Using intermediate value arguments at limits rather than finding explicit bounds

Again, I apologize for what looks like a very narrow question. But there's possibly a general principal at work here that I'm not grasping. I understand the answer provided for exercise 3 in chapter ...
10
votes
2answers
172 views

Given a cubic and quadratic share a root, prove $(ac-b^{2})(bd-c^{2})\geq 0$

Here is an interesting problem. Perhaps someone would be so kind as to give me a shove in the right direction?. If $ax^{3}+3bx^{2}+3cx+d$ and $ax^{2}+2bx+c$ share a common root, then prove that ...
10
votes
1answer
279 views

density of roots of a family of polynomials: $(1-x^2)^{v+n}$

My research has brought me to the following, very general problem. Given a fixed, but arbitrary, natural number, $\displaystyle v$, consider the following family of polynomials: The $\displaystyle ...
16
votes
5answers
4k views

Roots of Legendre Polynomial

I was wondering if the following properties of the Legendre polynomials are true in general. They hold for the first ten or fifteen polynomials. Are the roots always simple (i.e., multiplicity $1$)? ...