Questions about the set of values at which a given function evaluates to zero. For questions about "square roots", "cube roots", and such, consider using the (radicals) and (arithmetic) tag. For questions about roots of Lie algebras, use the (lie-algebra) tag instead.

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2
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2answers
54 views

Prove that a polynomial of odd degree in $ \Bbb R[x]\\$ with no multiples roots must have an odd number of real roots.

The coefficients of the polynomial are in the ring of real numbers. Prove that a polynomial of odd degree in $ \Bbb R[x]\\$ with no multiple roots must have an off number of real roots. I hate to ask ...
1
vote
2answers
59 views

Existence of real roots for vector quadratic equations

I have a vector quadratic equation of the form $\boldsymbol{x}^{T} \boldsymbol{A} \boldsymbol{x} + \boldsymbol{x}^{T} \boldsymbol{b} + c = 0$ where $\boldsymbol{A}$ is symmetric and for my particular ...
0
votes
2answers
45 views

Finding all the roots of a function - Numerical methods

I'm trying to find all the roots of a function f(x) without algebraically solving the function. What I have done so far: I attempted to use a numerical method, more specifically the secant method to ...
0
votes
4answers
145 views

Are there real solutions to $x^y = y^x = 3$ where $y \neq x$?

I need to solve the following equation for (x,y) $$x^y = y^x = 3$$ Everytime I run a numerical method for this problem, I get $$ (x,y) = (1.82546...,1.82546..) $$ I expect there to be a solution ...
2
votes
4answers
36 views

Can Extraneous Roots be Introduced by Elimination?

Suppose you have two equtaions: $$2xy + y^2 = 0$$ $$x^2 + 2xy + 1 = 0$$ Subtracting the second from the first yields $y^2 - x^2 - 1 = 0$. Isolating y, we discover that $y = \pm\sqrt{x^2 + 1}$. ...
0
votes
1answer
33 views

Non-linear equations Numerically

I have no clue on this question. Please help me. Find an approximate to $80^{1/3}$ correct within $10^{-5}$ using the Bisection method and false position method and compare the rates of convergence. ...
2
votes
1answer
36 views

Solving Non-linear equation for Computational math

Question is, the curve $y = x^3 - 2x^2 + x -1$ intersects the parabola $y = 2x^2 + 3x + 1$. Locate the intersection then use both False Position Method and Secant Method. (Numerically) I really need ...
1
vote
0answers
51 views

Convergence results for Durand-Kerner method

I've been using the mpmath library's (in Python) implementation of the Durand-Kerner method to find the roots of some "not small" polynomials (this is the polyroots function). Typically my ...
1
vote
2answers
39 views

Solve equation with exponentials

I'm trying to obtain $x$ in the following equation: $$ 1= ae^{bx}+ce^{dx} $$ with a,b,c,d known. What I did was to take the ln of all the equation, so I have: $$ \log\frac{1/ac}{b+d} = x $$ ...
0
votes
1answer
38 views

sum and product of roots of polynomials: finding equations for roots

this question pertains to the sum and product of roots. $x^2 + 2x + 5 = 0$ has roots $\alpha$ and $\beta$, hence $\alpha + \beta = 2$ and $\alpha \beta = 5$. Find the equation which has roots ...
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0answers
36 views

How to prove $a_{1}\sqrt[b_{1}]{c_{1}}+a_{2}\sqrt[b_{2}]{c_{2}}+…+a_{n}\sqrt[b_{n}]{c_{n}}$ is irrational?

Let's define the number $$A=a_{1}\sqrt[b_{1}]{c_{1}}+a_{2}\sqrt[b_{2}]{c_{2}}+.....+a_{n}\sqrt[b_{n}]{c_{n}}$$ where $a_{1}, a_{2}, ..., a_{n}$ are positive integers and $b_{1}, b_{2}, ..., b_{n}, ...
0
votes
4answers
123 views

How to solve a 6th-degree polynomial

How would you solve a polynomial with the equation $$ax^6 + bx^5 + cx^4 + dx^3 + ex^2 + fx + g = 0, \text{ ?}$$ with all of the coefficients being positive except for the constant.
0
votes
1answer
46 views

Correct Terminology for “Smallest” Number which could be Negative

I'm writing a paper and I'm doubting myself with a piece of terminology. I am finding roots of an equation, say {x1, x2}, where it's ambiguous which is greatest from the perimeters involved. So ...
3
votes
1answer
75 views

Coefficents of cubic polynomial and its least root

Let $x^3-(m+n+1)x^2+(m+n-3+mn)x-(m-1)(n-1)=0$, be a cubic polynomial with positive roots, where $m,n \ge2$ are natural nos. For fixed $m+n$, say $15$, it turns out that least root of the polynomial ...
4
votes
0answers
60 views

if $x^k-x\in\mathbb{Z}$ and $x^l-x\in\mathbb{Z}$, then $x\in\mathbb{Z}$?

is it true that for any $k,l\in\{2,3,4,\dots\}$, $k\neq l$, if $x\in\mathbb{R}$ satisfies $x^k-x\in\mathbb{Z}$ and $x^l-x\in\mathbb{Z}$, then $x\in\mathbb{Z}$? This is a generalisation of if ...
0
votes
1answer
20 views

Bounding the Roots of a Complex-Valued Function

Roots: $Z_1$= $\frac{v(1+ \alpha)+ \sqrt{v^2(1+\alpha)^2 -4 \alpha}}{2}$ $Z_2$= $\frac{v(1+ \alpha)- \sqrt{v^2(1+\alpha)^2 -4 \alpha}}{2}$ It is clear that $|Z_2| \leq|Z_1|$ However I'm stuck on ...
3
votes
4answers
86 views

Show that $8x^4 −16x^3 +16x^2 −8x+k = 0$ has at least one non-real root for all real $k$. Find the sum of the non-real roots

Show that $8x^4 −16x^3 +16x^2 −8x+k = 0$ has at least one non-real root for all real $k$. Find the sum of the non-real roots. Since this polynomial looks so symmetric, I think factoring it might ...
1
vote
1answer
34 views

Finding the number of solutions of the equation $2x^5- 6x^3 + 2x = 4x^4 - 6x^2 +1$ in the interval $I = [-2, 2]$

I have to find the number of solutions for the following equation on the interval $I=[-2,2]$ $$2x^5- 6x^3 + 2x = 4x^4 - 6x^2 +1$$ Now I know I have to put them all on one side and then use the ...
0
votes
1answer
64 views

Show that no ring containing R can contain a root of g(x) = 3x +1

Show that if $R = \mathbb Z_6$ and $g(x) = 3x + 1 ∈ R[x]$, then $R[x]/(g(x)R[x])$ does not contain a root of $g(x)$. More generally, show that no ring containing $R$ can contain a root of $g(x)$. ...
3
votes
1answer
54 views

Does the resolvent cubic of the quartic equation always have at least 1 positive real root

I have written some code to solve for the roots of a 4th order polynomial, and in the process, I noticed that the resolvent cubic always has at least one positive real root. I can't find anywhere ...
2
votes
2answers
60 views

Roots of trigonometric function.

I have a function: $ f(x) = (ax+b) \cdot \sin(x) + (cx+d) \cdot \cos(x) + e$ for which I want to determine the roots. I know that for $ax \cdot \sin(x) + cx \cdot \cos(x)$ the roots are ...
0
votes
1answer
45 views

why are the Bisection and Newton Method for finding roots complementary to each other?

my lecture note states that the bisection and newton method for finding roots are most of the time complementary to each other but I can not figure out why. I have basic understanding of both of the ...
3
votes
1answer
104 views

Closed form for the sole positive root of the polynomial ${x^\alpha } + {x^{\alpha - 1}} + \cdots + {x^3} + {x^2} -p$, $p > 0$

For a study I'm making about the minimum and maximum radial values of bounded orbits in a central force system with general power law forces, I came across this special polynomial equation: ...
1
vote
4answers
56 views

finding real roots by way of complex

I was given $$x^4 + 1$$ and was told to find its real factors. I found the $((x^2 + i)((x^2 - i))$ complex factors but am lost as to how the problem should be approached. My teacher first found 4 ...
3
votes
2answers
23 views

Finding a root approach with a polynomial

So, i'm solving last's year's exams in Mathematical Analysis and i've found one interesting. It says: The equation $e^{-4x}=5x^2$ has one root close to (nearby) 0. By approaching $e^{-4x}$(close to ...
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0answers
23 views

Zeros of this function?

Let $$f(z)=\gamma + z^{\beta_2-\beta_1}$$ where $\gamma\in \mathbb{R}$, $\beta_1\in \mathbb{Z}$, $\beta_2 \in \mathbb{Z}$ and $\beta_2 > \beta_1$. The variable $z$ takes complex values. Is there a ...
8
votes
1answer
133 views

Roots of iterations of polynomials

Let $f \in \Bbb Q[X]$ a polynomial, and let denote by $f^n$ the composition $\underbrace{f \circ \cdots \circ f}_{n \text{ times }}$. Let $R(f^n) \subset \Bbb C$ the roots of $f^n$. I'm interested in ...
0
votes
2answers
42 views

Find multiple roots of a three-dim system

Consider the three equations $$ y-x^2=0,\quad z+xy=0,\quad -y-z+x^2-xy+y^2+z^2-x^4=0. $$ How can I find multiple roots of this? Is it allowed to reduce the system as far as possible and then to find ...
1
vote
1answer
60 views

Is it possible to solve the following equation without using the Rational Root Theorem?

Given $f(x)=x^4+2x^3+2x^2-2x-3$, where $x-1$ is a factor of $f(x)$, how is it possible to solve $f(x)$ without the Rational Root Theorem? Here's my progress: $$f(x)=x^4+2x^3+2x^2-2x-3$$ ...
11
votes
2answers
200 views

Is $x$ irrational when $2^{x}+3^{x}=6$?

Is $x$ rational or irrational when $2^{x}+3^{x}=6$. How to show that?
2
votes
2answers
183 views

How to find $x$ when $2^{x}+3^{x}=6$?

$$2^{x}+3^{x}=6$$ How to find the real number x? I mean it's approximately $1.19$ bur can we write $x$ as the form of $a, b, c$ when $a^{x}+b^{x}=c$ in general. Maybe an infinite sum?
3
votes
1answer
29 views

Rational Points on Fibonacci-like Sequence of Polynomials

Let $\{a_n\}$ be a sequence of polynomials in $\mathbb{Q}[x,y]$ with $a_0=0,a_1=1$, and $$a_n=xa_{n-1}+ya_{n-2}$$ The first few look like $$a_3:y+x^2$$ $$a_4:2xy+x^3=x(2y+x^2)$$ $$a_5:y^2+3x^2y+x^4$$ ...
5
votes
3answers
59 views

Find the two values of $k$ for which $2x^3-9x^2+12x-k$ has a double real root.

Find the two values of $k$ for which $2x^3-9x^2+12x-k$ has a double real root. I've found one method which is to equate $$2x^3-9x^2+12x-k=2(x-r)^2(x-c)$$ Expanding and equating coefficients I ...
0
votes
1answer
76 views

Solution to the equation $x^3-3=2\sqrt{x+2}$

Solve the equation $x^3-3=2\sqrt{x+2}$. I have tried to let $t=\sqrt{x+2}$ then we have $$\begin{cases} x^3-3&=2t \tag 1\\ t^2 &=x+2 \end{cases}$$ But I've stuck here... Any help ...
3
votes
2answers
42 views

All zeroes of monic cubic $x^3+ax^2+bx+c$ are negative reals and $a\lt3$. Range of $b+c$?

$a,b,c$ are real numbers. I have to find the range of values of $b+c$. So, I started off by assuming $\alpha , \beta , \gamma$ as the roots. This gives us $\alpha \beta \gamma = -c$ and ...
0
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1answer
48 views

Prove that the equation $sin(x) = ax + b$ has at least one real root

I came across a question earlier this day, that I did not manage to solve. I have been asked to prove that the equation $\sin(x) = ax + b$ has at least one real root, for all $a, b$, where: 1) $a$ is ...
2
votes
1answer
28 views

Roots of polynomials combined with Trigonometric Functions

If $$ f(x) = x^2 + ax + d \cos x $$, where $a$ is an integer and $d$ is a real number, what are all possible values of the tuple $(a,d)$ such that $f(x)$ and $f(f(x))$ have the same set of real roots? ...
0
votes
1answer
37 views

Simplifying Rational Expressions in a Finite Field Extension

In Dummit and Foote's textbook one of the exercises is: Let $\theta$ be a root of $x^3-2x-2$ over $\mathbb{Q}$. Compute $\frac{1+\theta}{1+\theta+\theta^2}$ in $\mathbb{Q}(\theta)$. My approach ...
1
vote
2answers
51 views

magnitude of vector in algebra

I am trying to solve the following equation for x, in plain algebra this was easy $ y = x - \frac{1}{ x} $ $ x^{2} - yx - 1 = 0 $ $ x = \frac{-y \pm \sqrt (y^{2} + 4)}{2} $ However, throwing ...
1
vote
4answers
83 views

Find $\alpha^3 + \beta^3$ which are roots of a quadratic equation.

I have a question. Given a quadratic polynomial, $ax^2 +bx+c$, and having roots $\alpha$ and $\beta$. Find $\alpha^3+\beta^3$. Also find $\frac1\alpha^3+\frac1\beta^3$ I don't know how to proceed. ...
0
votes
1answer
56 views

Find a root of f(x) = 0, arccos & arcsin

Can someone please help me with this question? Let $f(x) = 2\arccos(\frac{x}{2}) + 6\arcsin(\frac{3}{2x}) - 2 \pi$ Find a root of $f(x) = 0$, that is a point x where $f(x) = 0$.
2
votes
0answers
43 views

Companion matrix of bivariate polynomial

A polynomial in one variable can be expressed as a companion matrix, of which the eigenvalues are the roots of the polynomial and which can be found by using e.g. QR decomposition or power iteration. ...
4
votes
1answer
103 views

root pattern of second degree polynomial

I'm considering the following 2nd degree polynomial for the case where the roots are complex conjugate. $ P(z) = z^2 + (f^2 + f q -2)z + (1 - f q) = (z - z_1) (z - z^*_1) $ where f and q are real ...
4
votes
3answers
111 views

What is the extraneous solution of $\sqrt a=a-6$?

What is the extraneous solution of $$\sqrt a=a-6$$ The roots are $9$ and $4$. So I'm assuming that $4$ is the extraneous solution because when you plug it in to the equation you wind up with $2=-2$. ...
4
votes
3answers
65 views

Is this quadratic pointing up or down? How do I know?

The equation is $-2x^2 + 4x + 30 = 0$. I simplified it to $-2(x^2 - 2x - 15)$. To know if it points up, I need to look at $ax^2$, and if $a > 0$ it is up and if $a$ is $< 0$ it is down. ...
1
vote
3answers
31 views

Which form of this quadratic do i use to solve intercept and range?

So my equation is: $-2x^2 + 4x + 30 = 0$ If I use this form to look at my y intercept, it will be 30. However, once I simplify it to: $x^2 - 2x - 15$, then my y intercept will be $-15$. Which one do ...
-1
votes
3answers
42 views

Solve for $x $(quadratic)

$$ 0=0.001 + \frac{-0.0018 x+0.009 x^2}{\left(\sqrt{0.04 - x^2}\right)^3}$$ Can't seem to figure out a way how to.
1
vote
1answer
52 views

What is the equation of the bottom half of the parabola $x + (y - 2)^2 = 0$?

A parabola has the equation: $$x + (y - 2)^2 = 0$$ I can't find the $y$ without getting the equation into some weird recursion.
2
votes
0answers
71 views

The convergence of the fixed-point iteration for solving a cubic equation

I have a third-grade polynomial of the form $Ax^3+Bx+C$ and I want to find its roots. I cannot use Gauss to guess the first root and it is not trivial, so I try this: $0=Ax^3+Bx+C$ and for a given ...
1
vote
0answers
50 views

Fastest way of find roots of polynomial defined over a finite field

Suppose we have polynomial $G(x)$ of degree $d$, where $d$ is a large value (e.g. $10^6$). The polynomial is defined over a finite field $\mathbb{F}_p$ for a large prime number $p$ (e.g. $p$ is ...