For questions about or involving the absolute value function.

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0
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1answer
43 views

How do I expand absolute values?

If we have this expression: $$f = uu-\left( u + \frac{\partial u}{\partial x} \delta x \right) \left( u + \frac{\partial u}{\partial x} \delta x \right)$$ we can expand it to this: $$f = u^2-\left( ...
0
votes
1answer
178 views

Logarithmic inequalities

Full disclosure: This is a homework problem, but my question is regarding a concept that came about during solving the problem, not the actual solution to the problem. Problem: Rewrite as geometric ...
0
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2answers
47 views

How to integrate absolute function

I have this absolute e-function, but I don't know how to calculate the integration $$ \int_{-2}^{2} e^{\frac{1}{2}j\omega |x|}dx $$ Any idea?
0
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0answers
34 views

Inequality with false solutions. Why? [duplicate]

When you have a question like $|x| = 3x – 2$, why do false solutions occur? if $x>0$, $x = 3x- 2$ $-2x = -2$ $x = 1$ If $x<0$, $x = -3x + 2$ $4x = 2$ $x = 1/2$ The $1/2$ solution is ...
0
votes
2answers
43 views

Absolute value question false solution

|x| = 3x – 2 Why does this statement eventually give you a solution that isn't valid. So this equation comes out: x = 3x - 2 2 = 2x x = 1 OR x = -3x + 2 4x = 2 x = 1/2 However 1/2 doesn't ...
0
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2answers
42 views

Absolute values in logarithms in a solution of differential equation

How have the moduli signs disappeared in the following step: $$\frac1{k}\left(\ln|g+kv| - \ln|g+ku|\right) = -t$$ Therefore $$ \ln\left(\frac{g+kv}{g+ku}\right) = -kt$$ $g$, $k$ and $u$ are ...
1
vote
1answer
36 views

Continuity of absolute value

Let $f(x)$ be a continuous function. Prove that $\left|f(x)\right|$ is also continuous. Is it correct to say that, by the reverse triangle inequality, $\left|f(x)-f(c)\right| \geq ...
0
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3answers
47 views

Absolute value question

Is it true that:$$\left|\,a-b+c-c\,\right|=\left|\,(c-a)+(c-b)\,\right|,$$ or, alternatively, $$\left|\,a-b+c-c\,\right| = \left|\,(a-c)+(c-b)\, \right|?$$ Why is this the case?
0
votes
1answer
65 views

Absolute value and credit card balance

I'm embarrassed to ask this question, but my child has the following homework question: "Use absolute value to describe the relationship between a negative credit card balance and the amount owed." ...
0
votes
2answers
44 views

$|a-b|+|b-c|+|c-a|=2(\max\{a,b,c\}-\min\{a,b,c\})$

Let $a,b,c ∈ \Bbb R$ Show that $|a-b|+|b-c|+|c-a|=2(\max\{a,b,c\}-\min\{a,b,c\})$ Not sure where to start
0
votes
0answers
16 views

Prove that the following function of binary random variables is monotonic

Consider a binary random variable $y$ over the space $\mathcal{Y} = \{+1, -1\}$ such that $\Pr(y = 1) = q$. Consider also $r$ binary random variables $y^1, \ldots, y^1$ over the space $\mathcal{Y}$ ...
2
votes
2answers
62 views

Strategy to solve absolute value inequality

I was wondering if there is any strategy to solve absolute value On both sides inequalities, for example, $$| x^2 -3x + 2 | < | x + 2|$$ Thanks, Eli
0
votes
1answer
46 views

Complex number in polar coordinates

I have to get $\Im$, $\Re$, the absolut value as well as the argument $\phi$ of the complex number $$z = \left(-\frac{1}{\sqrt2}+\sqrt\frac{3}{2}i\right)^8$$ I do this by transforming $z' = ...
0
votes
2answers
43 views

Why is the following simplification possible?

I have seen the following simplification: $$\left|\frac{1}{(-1-\frac{1}{n})^4 - 1}\right| = \frac{1}{\left|-1-\frac{1}{n}\right|^4 - 1}$$ I really don't have a clue why this is possible... I am ...
1
vote
0answers
31 views

Zeta function universality: How to compute the shift parameter for simple functions?

I've come across Zeta function universality. For a nice function $f$ in a nice subset $U$ of the complex strip between real $0$ and $1$, one can find a real $t$, such the zeta function $\zeta$ shifted ...
0
votes
1answer
24 views

Calculate the area that the following graphs form

I have been trying and trying to solve the following problem (I even used wolframalpha as an extra help, but no success, and I have like 100 calculations in my notebook): The Task: Calculate the ...
10
votes
6answers
1k views

How to calculate with absolute value.

Calculate:$$\frac{ \left| x \right| }{2}= \frac{1}{x^2+1}$$ How do I write the whole process so it will be correct? I need some suggestions. Thank you!
0
votes
0answers
52 views

about vectors norm

in the following article http://blanche.polytechnique.fr/~mallat/papiers/MallatPursuit93.pdf page 3 he say: $$y= \langle y , a_{k_0} \rangle a_{k_0} + R $$ with $a_{k_0}\in D$ with $\forall ...
0
votes
2answers
45 views

What is the Laurent series of the complex absolute value?

What is the Laurent series of the function $f(z) = |z|$? It seems to be ill defined at $z=0$. Are there any other expansion techniques applicable for this function at $z=0$?
1
vote
1answer
126 views

How to express 2 absolute values as a piecewise function??

I understand how to solve 1 absolute value as a piecewise function. $f(x)=|x-1|$ $$ f(x)= \begin{cases} x-1& \text{if }x\ge1\\ 1-x&\text{if }x<1 \end{cases} $$ But when a function ...
0
votes
1answer
57 views

Change of variables - integrals

\begin{equation} \text{Let $\hspace{3mm}$ }f(t) = 2\int_{b}^{\infty} \sqrt{\frac{1}{2\pi t}}e^{-x^2/2t}dx. \end{equation} I found that this integral can be written with change of variables can be ...
0
votes
1answer
58 views

Are there any $x,y,z$ in $\mathbb{R}$ for which the following equations hold?

Are there any $x,y,z \in \mathbb{R}$ for which the following equations hold? $$|x+1| \leq 2\\ |y+1| \leq 3\\ |y-z| \leq 1$$ With the given we know that $x$ is between $[-3,1]$, $y$ is between ...
1
vote
1answer
39 views

Proving a claim $|c_n e^{in\theta}| = |c_n|$

I'm studying about Fourier series from a book called "Fourier series and its applications" by Folland and on page 40, the author makes the claim that: $$|c_n e^{in\theta}| = |c_n|,$$ where $n$ is an ...
0
votes
2answers
228 views

Prove that the absolute value of a product is the product of the absolute values of factors.

Theorem. $|a||b|=|ab|$ Proof. Applying the definition of absolute value, the left hand side of the equation could be either $a\times(-b)$ or $(-a)\times(b)$ or $a\times b$ or $(-a)\times(-b)$. For ...
0
votes
4answers
153 views

Find $z$ such that $|z+1|+ |z-1|=4$

I have this problem: Find all points of the complex plane wich satisfy: $$|z+1| + |z-1| = 4 $$ I know this is an ellipse with foci 1 and -1, and i know the answer is : $$3 x^2+4 y^2 \leq 12$$ but ...
3
votes
3answers
108 views

Proving continuity of a absolute value function

How can i prove the function $f: x \mapsto x|x|$ is continuous over $\mathbb{R}$ using epsilon-delta definition. I've tried: Given a certain $\epsilon$ we want to prove that there exists a $\delta$ ...
0
votes
2answers
103 views

Minimizing the sum of absolute values with a linear solver

I need a linear program to minimize the sum of several absolute values, but the inclusion of an absolute value means the linear solver won't work. I know there are ways around using an absolute value, ...
0
votes
1answer
57 views

Problem with absolute value

Say that $|\sqrt{x}-1| < \epsilon$. I am having a problem with handling this inequality. I want to exclude x. I. $|\sqrt{x}-1| < \epsilon$ $|\sqrt{x}| - |1| \leq |\sqrt{x}-1| < \epsilon$ ...
1
vote
2answers
52 views

Proof by contradiction: $c<a<d \wedge c<b<d \to |a-b|<d-c$

Let be $a,b,c,d \in \mathbb{R}$, I must proof "$c<a<d \wedge c<b<d \to |a-b|<d-c$". Proof by contradiction: I have $|a-b|\geq d-c$, therefore $a-b \leq c-d \vee a-b \geq d-c$ (or $a-c ...
2
votes
1answer
47 views

Solving inequation with two absoulte values

I need to solve the following inequation: $$ |x| \cdot |x-1|-1>-x\\ $$ I cant get the correct result. I tried to solve it like this: $$ |x| \cdot |x-1|-1>-x $$ I know that I can write $|x ...
2
votes
2answers
73 views

$|x|=\max\{-x,x\}=\max\{-x,x,0\}$?!

Let $x \in \mathbb{R}$, $|x|=\max\{-x,x\}$, is correct also $|x|=\max\{-x,0,x\}$? Thanks in advance!
0
votes
3answers
72 views

Absolut value of cubic polynomial roots lower than 1

Assume we have a cubic polynomial $ x^3 +bx^2+xc+d=0 $, with b,c,d real numbers. Let $x_1, x_2, x_3 $ be the roots, either real or complex. What is the relation of the coefficients b,c and d in ...
1
vote
2answers
46 views

I want to check that $\left|\left|a+b\right|-\left|a\right|-\left|b\right|\right|\leq2\left|b\right|\forall a,b\in\mathbb{R} $.

I want to check that $\left|\left|a+b\right|-\left|a\right|-\left|b\right|\right|\leq2\left|b\right|\forall a,b\in\mathbb{R} $. It 's equivalent to ...
-4
votes
3answers
70 views

How to solve this: $|3-x|\ge2$ [on hold]

How to solve $|3-x|\ge2$ ? I know that if $|x| < y$, then $-y < x < y$. But in this case what to do? Thanks. Here, $|x|$ is the absolute value of $x$.
4
votes
4answers
105 views

Let $x$ be in the set of real numbers $\mathbb{R}$ and let $f(x)=|2x-1|-3|2x+4|+7$ be a function, write $f(x)$ without the absolute value.

Let $x$ be in the set of real numbers $\mathbb{R}$ and let $f(x)=|2x-1|-3|2x+4|+7$ be a function, write $f(x)$ without the absolute value. I thought of it this way: $$f(x)=\begin{cases}2x-1-3(2x+4)+7 ...
0
votes
2answers
115 views

Absolute value of a number [closed]

Is there a formula for finding the absolute value of a number? Or finding which is greater of the two, let say A and B, without inspecting A and B itself?
0
votes
1answer
27 views

Absolute Value Inequality - Precision

So I was writing a computer program, which is supposed to check whether $x$, an approximation of $\sqrt{a}$, is close enough to $\sqrt{x}$. Since these definitions aren't very precise, I defined ...
14
votes
4answers
525 views

How find this inequality $\max{\left(\min{\left(|a-b|,|b-c|,|c-d|,|d-e|,|e-a|\right)}\right)}$

let $a,b,c,d,e\in R$,and such $$a^2+b^2+c^2+d^2+e^2=1$$ find this value $$A=\max{\left(\min{\left(|a-b|,|b-c|,|c-d|,|d-e|,|e-a|\right)}\right)}$$ I use computer have this $$A=\dfrac{2}{\sqrt{10}}$$ ...
3
votes
2answers
99 views

How does the triangle inequality work for $|x-y|$?

I know that $|x+y|\leq |x|+|y|$... But is it similar for $|x-y|$? That is, is $|x-y|\leq |x|+|y|$? I ask because of the following: $x-y=x+(-y)$, so $|x+(-y)|\leq |x|+|-y|=|x|+|y|$ Is it possible ...
-2
votes
1answer
114 views

Example of a function $f$ which is nowhere continuous but $|f|$ should be continuous at all points [duplicate]

So I had an exam today and one of the questions were: Give an example of a function $f$ which is nowhere continuous but $|f|$ should be continuous at all points. At first I had no idea how to do it ...
1
vote
1answer
48 views

When is $|f(x)|$ equivalent to $f(|x|)$

Specifically for functions of a complex variable. Are there any rules of thumb?
1
vote
0answers
321 views

Properly Solving Absolute Value Inequality and Quadratic Inequality Problems

How do I solve the following absolute value inequality and inequality problems properly? 1) $\newcommand\abs[1]{|#1|}\abs{2x+9}>x$ Solving this problem algebraically, I get When $x > 0, x ...
1
vote
1answer
49 views

What is the Fourier transform of an M like function

Given the function $$ f(x)= \begin{cases} \vert x \vert& \text{, for }\;\vert x\vert\le M \\ 0 & \text{, otherwise} \end{cases} $$ for some constant $M$. What would be the form for the ...
0
votes
0answers
20 views

Derivative of squared Fourier transform

I haven't found any relative to this, so I would like to get some help. I have a function $h(x) = |\mathcal{F} [P(x) e^{ic+iZ(x)a}]|^2 $ and I would like to find the derivative with respect to the ...
0
votes
2answers
35 views

$\iint_V |y-x^{2}| \operatorname{d}x \operatorname{d}y$ with $V = [-1,1] \times [0,2]$

it's especially difficult because i don't understand how to integrate absolute value terms. I only know that if you function, say $x^{2}-1$, is below the $x$-axis i need to integrate $1-x^2$ between ...
1
vote
1answer
44 views

limit of an absolute sequence: ${b_n} = |{a_n} - 1|$

$$\eqalign{ & \mathop {\lim }\limits_{n \to \infty } {a_n} = 3 \cr & {b_n} = |{a_n} - 1| \cr} $$ Hence, $$\mathop {\lim }\limits_{n \to \infty } {b_n} = |3 - 1| = 2$$ Is it right to ...
0
votes
2answers
86 views

Absolute Value Properties

I'm attempting to prove that $|x|-|y| \le |x-y|$. I've come up with the following proof. The proof relies on these results obtained from previous exercises: $-|x| \le x \le |x|$ ${|x-y|=|y-x|}$ ...
0
votes
1answer
63 views

usage of absolute value within natural log in solution of differential equation

y=2^x sinx rewriting, |y|=2^x |sinx| my questions, before taking the natural log for both sides and rearrange why do we need to rewrite using absolute value? why this particular question need to have ...
0
votes
1answer
50 views

Help solving a problem with inequalities with absolute values

I have these statements presented: $|x - x_0| < \frac{\epsilon}{2(|y_0| + 1)}$ , $|x - x_0| < 1$ , $|y - y_0| < \frac{\epsilon}{2(|x_0| + 1)}$ And I must prove that: $|xy - x_0y_0| < ...
0
votes
4answers
70 views

Inequalities and absolute values

My book asks that if $$-5\leq x\leq 1$$ then find the boundaries of absolute value of $x$. Can you please help me in finding that?