Absolute values Definition and 77 Threads

In mathematics, the absolute value or modulus of a real number x, denoted |x|, is the non-negative value of x without regard to its sign. Namely, |x| = x if x is positive, and |x| = −x if x is negative (in which case −x is positive), and |0| = 0. For example, the absolute value of 3 is 3, and the absolute value of −3 is also 3. The absolute value of a number may be thought of as its distance from zero.
Generalisations of the absolute value for real numbers occur in a wide variety of mathematical settings. For example, an absolute value is also defined for the complex numbers, the quaternions, ordered rings, fields and vector spaces. The absolute value is closely related to the notions of magnitude, distance, and norm in various mathematical and physical contexts.

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  1. R

    B Binary variables (Absolute values)

    Hello, According to https://www.fico.com/fico-xpress-optimization/docs/latest/mipform/dhtml/chap2s1.html?scroll=ssecabsval the formula for absolute values are : y = | x1 - x2| for two variables x1, x2 with 0 ≤ xi ≤ U Introduce binary variables d1, d2 to mean d1 : 1 if x1 - x2 is the positive...
  2. C

    Quadratic inequalities with absolute values

    I was given a problem to solve that goes like this ##\frac{3}{|x+3|-1}\geq |x+2|## . I got the correct solution for all possible cases and here they are; for ##|x+3|\geq0## and ##|x+2|\geq## i got ##x\epsilon <-2, -2\sqrt{3} ]## and for ##|x+3|\leq0## , ##|x+2|\leq0## I got ##x\epsilon [-5...
  3. brotherbobby

    Solving an inequality involving absolute values

    Problem Statement : I copy and paste the problem as it appeared in the text to the right. Attempt (mine) : I copy and paste my attempt using Autodesk Sketchbook##^{\circledR}## below. I hope the writing is legible. My answer : I have three answers and confused as to which of them hold...
  4. brotherbobby

    Solving an equality with absolute values

    Problem statement : Let me copy and paste the problem to the right as it appears in the text. Solution attempt (mine) : There are mainly three cases to consider. (1) ##\boldsymbol{x\ge 3\; :}## Using the relevant equations given above, the problem statement reduces to $$x-3+x-2 = 1\Rightarrow...
  5. N

    Simplify An Expression Containing Absolute Values

    See attachment. I don't understand the solution given by David Cohen. I am sure this is a shortcut explanation. I don't like shortcut explanations. 1. What in the problem indicates that x > 1? 2. What in the problem indicates that x < 2?
  6. jk22

    I CHSH inequality : renaming and absolute values

    In some derivations of the CHSH inequality, https://en.m.wikipedia.org/wiki/CHSH_inequality, the following arises : $$CHS=\int A(a,l1)B(b,l1)dl1-\int A(a,l2)B(b',l2)dl2+\int A(a',l3)B(b,l3)dl3+\int A(a',l4)B(b',l4)dl4\\ =\int A(a,l)B(b,l)dl1-A(a,l)B(b',l)+A(a',l)B(b,l)+A(a',l)B(b',l)dl$$ 1)...
  7. W

    I Proof of a Lemma regarding absolute values

    Hi all, There's this proof that I've been trying to wrap my head around but it just doesn't seem to sink in. I've attached a screenshot below. Many thanks in advance! Consider Case 1. There is a step that goes $$\text{Then} \ |r| = r$$ $$Then -|r| \leq |r| \ \text{and} \ r \leq |r|$$ Why is...
  8. P

    Solving absolute values of trigonometry

    Homework Statement Homework EquationsThe Attempt at a Solution 2sin3x=1 OR 2sin3x= -1 sin3x=1/2 sin3x= -1/2 From the unit circle and in accordance with the domain there are 3 solutions (B) But the answer is (C) HOW?
  9. B

    B Solving Absolute Value Inequalities: How to Define Cases

    Hi there, I'm having trouble understanding this math problem: |x| + |x-2| = 2 The answer says its: 0<=x<=2 I understand you need different "cases" in order to solve this. For example, cases for when x is less than 0, when x-2 is less than 0, etc. Thanks, blueblast
  10. TheSodesa

    How to Fourier-transform e^(-2|t|)?

    Homework Statement Determine the Fourier-transfroms of the functions \begin{equation*} a) f : f(t) = H(t+3) - H(t-3) \text{ and } g : g(t) = \cos(5t) f(t) \end{equation*} and \begin{equation*} b) f : f(t) = e^{-2|t|} \text{ and } g : g(t) = \cos(3t) f(t) \end{equation*}Homework Equations The...
  11. JuanC97

    I Why Does Integrating |f(x)| Differ from Integrating f(x)?

    I know that \sqrt{f(x)^2} = |f(x)| However... I've just noticed that integrals of expressions like this are usually assumed to be equal to the integral of f(x) without the absolute value. I'd like to know how that's possible. Is weird for me to consider those expressions; specially because of...
  12. A

    Absolute function into piecewise function

    Homework Statement Write F(x)= x2-5|x| as a piecewise function Homework EquationsThe Attempt at a Solution I was writting it out and came to Fx= x2-5(x) and x2-5(-x) but my book says that it comes out to be x2-5 x2-5(-x) I imagine there is a very simple reason why the x in the first one...
  13. T

    MHB Proving absolute values theorems

    For all real numbers $x$ and $y$ , if $x + y >= 0$ then $|x + y| = x + y$. How would I prove this? My textbook just assumes this to be true.
  14. barryj

    How to solve absolute value equation with two absolute values

    How does one solve an equation with two absolute value functions as below My algebra book does not show how to solve with two abs functions. 2|4x-1| = 3|4x+2| I thought this might work.. |4x-1|/|4x+2| = 3/2 then |(4x-1)/(4x+2)| = 3/2 and solve the normal way..
  15. P

    Limits involving absolute values

    This is actually a physics problem, but since my question is really about the math involved, I decided to post it in the calculus subforum. I'm supposed to get from the term: $$\lim_{\Delta t → 0} |\vec{v}_r (t + \Delta t)| \frac{\sin \Delta \theta}{\Delta t}$$ To: $$v_r (t) \frac{d\theta}{dt}$$...
  16. patrickbotros

    Absolute Values in Separable Differential Equations

    When solving a separable differential equation, my textbook says this: ln|v-49|=-t/5+C→ |v-49|=e-t/5+C→ v=49+ce-t/5 What happened to the absolute values? I think it has something to do with the exponential always being positive.
  17. S

    How can I solve a one-sided limit without using l'Hopital's rule?

    Homework Statement Find the ## lim _{x-> -1+} sqrt(x^2-3x)-2/|x+1| ## Homework EquationsThe Attempt at a Solution I can only solve it using l'hopital rule and would like to know the steps of solving it without using it. ## lim _{x->-1+} (2x-3)/|1|= -5/4 ##
  18. T

    Fortran FORTRAN 77 input absolute values

    How to input absolute values in FORTRAN77? This was the code I used READ *,H PRINT *,H The input I gave was 0.01 But the output I got was 0.00999999978.
  19. Dethrone

    MHB How Do Absolute Values Affect Integration?

    I feel like I'm asking the weirdest questions that most people don't ask, but here it is. Suppose we have this integral (I made it up): $$\int \sqrt{x^4+2x^3+x^2}$$ Now, I feel most people would say the answer is simply, $\frac{1}{3}x^3+\frac{1}{2}x^2+C$. But technically, that is only true...
  20. Mogarrr

    Integrating functions with absolute values

    To find E |X| of a cauchy random variable, I need to integrate \int_{-\infty}^{\infty}\frac1{\pi}\frac{|x|}{1+x^2}dx . From the definition of absolute value, we have \int_{-\infty}^0\frac1{\pi}\frac{-x}{1+x^2}dx + \int_0^{\infty}\frac1{\pi}\frac{x}{1+x^2}dx (I think). But, the very next...
  21. D

    Is the Inequality with Absolute Values |x+y| ≤ |x| + |y| True?

    Wonder if this is true or just mistype: |x+y| \leq |x| +|y| If this is true how to proof because cannot find it out anywhere written Regards
  22. B

    When is the root of a number both negative and positive?

    Homework Statement I have a simple problem with roots and absolute values. When is the root of a number both negative and positive? Is only the equation of a number say f(x) = √x both the negative root and the positive root? Homework Equations If a = 1; b = -2, och x = a2√(ab-b2+2) Why is x...
  23. Y

    Converting a linear optimization problem with absolute values

    Homework Statement Here is an alternative approach to handling absolute value terms as the decision variables: abs(x) is the smallest value z that satisfies x \leq z and -x \leq z. Using this,convert the following into a lp Min 2x1 + 3abs(x2) S.T x1 + x2 \geq 6 Homework Equations Here is a...
  24. R

    Graph of double absolute values

    Homework Statement |x| + |y| ≤ 1 What is the region in the plane that solves this inequality? Homework Equations The Attempt at a Solution I first tried graphing it by isolating the y variable |y| ≤ -|x| + 1 Then I looked at the hint we were given, which was to assume that x and y...
  25. 1

    Looking for a simple generalization regarding absolute values

    Hi all, I was working on a proof that essentially worked because: |x-y|+|y-z| >= |x-y+y-z| I knew this was true because, but I'm looking for a generalization in a way that I could write in a proof. Can you say that when comparing two expressions of addition/subtraction that are...
  26. E

    Can you please teach me the properties of absolute values

    I am new in the field of science please can you help me. I would I appreciate it. I am not that knowledgeable.
  27. I

    Confused About Squareroots & Absolute Values

    $${ x }^{ 2 }=4\\ \sqrt { { x }^{ 2 } } =\sqrt { 4 } \\ |x|=2$$ According to my professor, in the above case, the absolute value gives two solutions: ##x=±2## Consider the discriminant in the quadratic formula: $$x=\frac { -b±\sqrt { { b }^{ 2 }-4ac } }{ 2a } \\ Let\quad { z }^{ 2 }={ b }^{ 2...
  28. D

    Evaluating the integral of absolute values

    Homework Statement ∫(0 to 3pi/2) -7|sinx|dx Homework Equations The Attempt at a Solution I am not sure how to treat it as it has an absolute value i assumed that you could remove the -7 to get -7∫|sinx| dx then integrate sinx into -cosx but since there is absolute...
  29. P

    Intuitive reason absolute values are used for transformations in statistics?

    this isn't really homework, but I was just wondering if someone could offer an intuitive reason as to why when random variables are transformed, we use absolute values of derivative of those functions, as opposed to the functions themselves?
  30. ElijahRockers

    Integrating absolute values over infinity

    Homework Statement Find <x> in terms of X0 if X0 is constant and \Psi(x) = \frac{1}{\sqrt{X_0}}e^{\frac{-|x|}{X_0}} and <x> = \int^{\infty}_{-\infty}{\Psi^* x \Psi}dx where Psi* is the complex conjugate of Psi. Since there is no imaginary component, this is effectively Psi2. so, from...
  31. P

    Inequality with two absolute values

    Homework Statement Find all real values of x that satisfy the following inequality. Homework Equations |x-3| > |x + 1| The Attempt at a Solution Splitting up the inequality into cases I get: 1. |x-3| > x + 1 and 2. |x-3| < -x - 1 1. x-3 > x + 1 or x-3 < -x - 1...
  32. R

    Why do absolute values appear in the simplification of square roots?

    Homework Statement Simplify. a) \sqrt{x^6} b) 8 \sqrt{x^7y^{10}} - 10 \sqrt{x^7y^{10}} For b, it's y^10. I can't make it look right for some reason. Mod note: Fixed the exponent. Homework Equations The Attempt at a Solution I can simplify all of them but I don't know when or where I need to...
  33. T

    An inequality with absolute values

    Homework Statement Solve Ix+3I>2 *I is used for absolute value notation The Attempt at a Solution Considering both a) Ix+3I > 0 then Ix+3I= x+3 b) Ix+3I < 0 then Ix+3I= -(x+3) when solved this would yield to; a) x>-3 and x>-1 b) x<-5 and x<-3 from my general reasoning i...
  34. V

    Replacement of Squaring in Variance Equation: Benefits?

    The variance equation basically sums up all the distances between each data value and the mean of the set. The interesting thing is that each distance and squared for a reason that I believe is to make the distance positive, but why don't the statisticians just take the absolute value of each...
  35. Saladsamurai

    Proofs: Absolute Values and Inequalities

    Homework Statement I am wondering if the general approach to these proofs involving absolute values and inequalities is to do them case-wise? Is that the typical approach (unless pf course you see some 'trick')? For example, I have: Prove that if |x-xo| < ε/2 and Prove that if |y-yo| <...
  36. K

    System of equations incl. complex and absolute values

    Homework Statement I'm currently implementing an algorithm in Matlab, however, I've hit a bump, I'm trying to solve the following system of equations: Known variables = a, b, c, d[complex] Unknown variabls = fs, fd, fv, alpha My problem is what to do with the |alpha| since I can't get...
  37. G

    Complex inequality with absolute values

    Homework Statement Determine the values of z \in \mathbb{C} for which |z+2| > 1 + |z-2| holds. Homework Equations Nothing complicated I can think of. The Attempt at a Solution For real values this holds for anything greater than 1/2. If I could figure out the boundaries of the...
  38. P

    Absolute values resulting in diff-eqs

    Homework Statement Consider a simple first-order linear differential equation, such as y' + \tan x y = 0 With initial condition y(0)=C for some constant C. Find all solutions y which satisfy this differential equation on the entire real line. Homework Equations General method for...
  39. W

    Inequalities involving division of two absolute values

    Homework Statement How to solve x for these inequality? Homework Equations |x-2|/|x+3|> (x+2) / (x+1) The Attempt at a Solution (x - 2)/(x + 3) > (x + 2) / ( x+1) the left side holds the condition that is x >= 2 however, I wonder the next step. should I crossly multiply so...
  40. S

    Solving integrals with absolute values

    Homework Statement solve the integral [abs(x+1)(3+abs(x))]/(x+1) between -3 and 1 Homework Equations The Attempt at a Solution when x<-1 then [abs(x+1)(3+abs(x))]/(x+1) = [-(x+1)(3-x)]/(x+1) = -(3-x) when -1<x<0 then [abs(x+1)(3+abs(x))]/(x+1) = (x+1)(3-x)/(x+1) = 3-x when x>0...
  41. S

    Integration with absolute values

    Homework Statement if f(x)=abs(x-2) and g(x)=abs(x), then solve the integral from -1 to 3 of abs(f(x)-g(x))dx Homework Equations The Attempt at a Solution resolved absolute values: when x<0, abs(x-2)-abs(x) = -x-2+x = 2 when 0<x<1, abs(x-2)-abs(x) = (-x+2)-x = 2-2x when 1<x<2...
  42. S

    How to Solve Nonhomogeneous Euler Equations with Absolute Values?

    Homework Statement Solve the IVP (x^2)y'' + 4xy' - 40y = x^6 for y(1) = 10, y'(1) = 1Homework Equations not so much "equations" but here I try to use variation of parameters to get the particular solution.The Attempt at a Solution FOR THE HOMOGENEOUS SOLUTION: using the substitution y = x^r...
  43. J

    Solving equation containing absolute values

    Homework Statement I have this equation |2x+7| - |6-3x| = 8. The step I did is to replace the || with () and then solve the equation 2x+7-6+3x = 8 X = 7/5 But how do a go about solving for the second solution? With one absolute value I would |2x + 7| = 8 2x + 7 = +-8 2x = -7...
  44. J

    Understanding Absolute Values.

    Hey Guys! I've frequently come by this forum and have finally joined it in hopes that I could get some more conceptual insight in understanding math. One thing that I have trouble with is absolute values. I understand that: |x|= \sqrt{x^2} .. and how it can be defined given restrictions on...
  45. A

    Minimizing Sum of Absolute Values

    Hello all, I am trying to solve a problem based on some computer programming task I am trying to solve, and I have encountered a situation I am having trouble continuing.. Given a function f(x)=|1-x| + |0.5-2x| ... How can I find it's minimum efficiently? This sum may extend to 4 or 5...
  46. M

    Proofs with continuity and absolute values

    Homework Statement -F is a continuous function on [0,1], so let ||f|| be the maximum value of |f| on [0,1] a. Prove that for any number c we have ||cf|| = |c|\ast||f|| b. Prove that ||f + g|| \leq ||f|| + ||g||. c. Prove that ||h - f|| \leq ||h - g|| + ||g - f|| Homework Equations Based...
  47. W

    HELP Absolute Values on a Complex Plane

    Homework Statement Draw |z| on a complex plane, where z = -3+4i Homework Equations N/A The Attempt at a Solution [PLAIN]http://img530.imageshack.us/img530/1786/aaakr.jpg Can anyone please tell me which answer is correct? Both of them have a moduli of 5. So should the circle...
  48. N

    Confused about equations with absolute values

    My calc book rewrites this equation: |y|=e^c|x| As this: y=\pm e^cx But that doesn't really make any sense to me. I know I should understand why we're allowed to do that, but I don't. Could someone please try to explain it to me? I really appreciate your help, thanks!
  49. J

    Absolute Values and Inequality understanding

    Homework Statement I saw this in my real analysis textbook and I have been trying to understand how this equation \left | x-c \right |< 1 you can get this: \left | x \right |\leq \left | c \right | + 1 Homework Equations I wanted to know what steps made this possible ...
  50. M

    Proving Non-Continuity at (0,0) for f(x,y) = |xy|

    Homework Statement Let f(x, y) = |xy|. I want to prove that f is not continuous at (0,0). The Attempt at a Solution To prove that f is not continuous at (0,0) I think I need to show that \lim_{(x, y) \to (0, 0)}|xy| \neq 0 I'm a little confused about the |absolute value|...
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