Limit Definition and 999 Threads

  1. NihalRi

    What is the proof for the limit superior?

    Homework Statement 2. Relevant equation Below is the definition of the limit superior The Attempt at a Solution I tried to start by considering two cases, case 1 in which the sequence does not converge and case 2 in which the sequence converges and got stuck with the second case. I know...
  2. Y

    Help Taking the Limit as K goes to infinity

    Homework Statement Evaluate the limit as K goes to infinity of s_1,2 (K) Homework EquationsThe Attempt at a Solution Apparently my value for plus the square root is incorrect, apparently the correct answer is 1. Apparently my value for minus the square root is correct, it's negative...
  3. shrub_broom

    Prove that the limit of a sequence exists

    Homework Statement suppose that 0≤xm+n≤xm+xn for all m,n∈ℕ, prove that the limit of xn/n exists when n tends to infinity. Homework EquationsThe Attempt at a Solution I get that xn is bounded by zero and x1. And I guess that xn is monotonous but i find it hard to prove. Or maybe there is...
  4. D

    Approximations with the Finite Square Well

    Homework Statement Consider the standard square well potential $$V(x) = \begin{cases} -V_0 & |x| \leq a \\ 0 & |x| > a \end{cases} $$ With ##V_0 > 0##, and the wavefunctions for an even state $$\psi(x) = \begin{cases} \frac{1}{\sqrt{a}}cos(kx) & |x| \leq a \\...
  5. Mr Davis 97

    Showing that a limit does not exist

    Homework Statement Let ##f(x) = 0## if ##x## is rational and ##=1## of ##x## is irrational. Prove that ##\lim_{x\to a} f(x)## does not exist for any ##a##. Homework EquationsThe Attempt at a Solution I need help setting this one up. I was thinking that maybe I can argue by contradiction and...
  6. J

    MHB Limit of Function at x=0: Does Not Exist (DNE)

    hello I have an exercise which says: Evaluate the following limit. Enter -I if your answer is −∞, enter I if your answer is ∞, and enter DNE if the limit does not exist. limx→0[(1/(7x)−(1)/((e^(7x))−1)] e power 7x when I follow the graph for 1/7x the limit does not exist (goes to...
  7. M

    I Proving the limit of a sequence from the definition of limit

    Say that we are asked to prove, using the definition of limits, that the sequence ##\frac{4n^2+3}{n^2+n+2}## tends to ##4## as ##n## tends to infinity. The following is a screenshot of the solution I found in a YouTube video: (Note that in the definition above, "g" denotes the limit - in this...
  8. Mr Davis 97

    I Result regarding signs and a limit

    Suppose that ##f : \mathbb{R} \to \mathbb{R}## is differentiable at ##a\in\mathbb{R}##. Is it true that if ##\lim_{x\to a}\frac{f(x)-f(a)}{x-a}>0## and ##x>a## then ##f(x)>f(a)##? I'm trying to find a counterexample to show that its false because I think it is, but I'm having a hard tome doing...
  9. K

    Limit of Taylor Polynomial for Tn(x) as n Approaches Infinity

    Homework Statement Let Tn(x)=1+2x+3x^2+...+nx^(n-1) Find the value of the limit lim n->infinity Tn(1/8).The Attempt at a Solution How do I solve this? I know how to write the polynomial as a series, but not sure how if this is the best way of finding the limit.
  10. A

    MHB A generalization of the limit definining \$e\$.

    I was thinking of generalizing the limit of $\lim_{n\to \infty} (1+x/n)^n=\exp(x)$. What do we know of $$\lim_{n_1\to \infty , n_2 \to \infty , \ldots , n_k \to \infty } (1+\prod_{i=1}^k x_i/n_i)^{\prod_{i=1}^k n_i}$$?
  11. Y

    MHB Calculus 2 (Power Series) when the limit is zero by root test

    Hi guys! Here's a problem i was working on. I solved it by root test and got absolute value of x on the outside of the limit and the limit equaled zero. Is it wrong to multiply the outside absolute value by the zero I got from the limit? or is that okay? In general, when we are solving power...
  12. M

    Is this Proof for an Infinite Limit Correct?

    <Moderator's note: Moved from a technical forum and thus no template.> 1. Homework Statement Is this proof correct? Let K>0, and choose N such that N >= K2, then for all n in the naturals, and n>=N, sqrt(n)+7>=sqrt(N)>=K Is this proof correct? Please tell me
  13. mbrmbrg

    Limit Switch, Servo Motor Resources

    I need a better understanding of limit swtiches and servo motors than I'm getting from Wikipedia :) Any website/textbook recommendations? (My background is physics.) TIA!
  14. karush

    MHB Limit $\frac{f(x)}{g(x)}$: Solve w/ L'H Rule

    Consider the following limit where L'H Rule was correctly applied twice Determine the functions f'(x), g'(x), f(x), and g(x) needed to result in the limit given. \begin{align*}\displaystyle \lim_{x \to 0}\frac{f(x)}{g(x)} \overset{\text{L'H}}=& \lim_{x \to...
  15. F

    I Infinity: The Limit Concept and Cantor Transfinites

    Supposedly, infininity has been purged from mathematics. Both the infinitely small and the infinitely large have been replaced by the idea of a "limit." For example, a series x0+x1+x3+... is not considered to be a literal infinite sum with infinite terms but only the limiting value of an...
  16. T

    Difference between Elastic Limit & Yield Point

    Hi All I am trying to understand a stress / strain curve for a ductile material. But I am struggling with understanding the difference between the Elastic Limit and the Yield Point. I define these terms as:- Elastic Limit - Is the point on the stress/strain curve where the material will...
  17. evinda

    MHB Convergence of Sequences: Exploring the Limit Inside

    Hello! (Wave) I want to check the convergence of the sequences $\left( \left( 1+\frac{1}{\sqrt{n}}\right)^n\right)$, $\left( \left( 1+\frac{1}{2n}\right)^n\right)$. We know that $e^x=\lim_{n \to +\infty} \left( 1+\frac{x}{n}\right)^n$. We have that $\lim_{n \to +\infty} \left(...
  18. evinda

    MHB Doesn't it suffice to pick the limit of the sequence?

    Hello! (Wave) Let $(a_n)$ be a sequence of real numbers such that $a_n \to a$ for some $a \in \mathbb{R}$. I want to show that $\frac{a_1+a_2+\dots+a_n}{n} \to a$. We have the following: Let $\epsilon>0$. Since $a_n \to a$, there is some positive integer $N$ such that if $n \geq N$, then...
  19. K

    I Understanding the Limit Notation: Is f(rh,h) the Same as f(r+h)-f(h)?

    Limh→0+ (f(rh,h))/h Is the f(rh,h) part the same as f(r+h)-f(h)? I have never seen this before and googling for a long time didn't help, there are no videos with this notation and it's not in my book so, am I just to assume it is? because it doesn't look like it should be the same. Anyone know...
  20. Mr Davis 97

    Limit Investigation: (-1)^n( r^n-r^{-n}) with r ≠ 0 for n approaching infinity

    Homework Statement Identify the following limits. Indicate if they do not exist. Assume ##r\ne 0##. ##\displaystyle {\lim_{n\to\infty}}(-1)^n( r^n-r^{-n})## ##\displaystyle {\liminf_{n\to\infty}}(-1)^n( r^n-r^{-n})## ##\displaystyle {\limsup_{n\to\infty}}(-1)^n( r^n-r^{-n})## Homework...
  21. karush

    MHB 241.19 the e d definition of a limit.

    prove the statement using the $\epsilon,\delta$ definition of a limit. $$\lim_{{x}\to{1}}\frac{2+4x}{3}=2$$ so then $$x_0=1\quad f(x)=\frac{2+4x}{3}\quad L=2$$ now $$0<|x-1|<\delta\quad\text {and}\quad\left|\frac{2+4x}{3}-2\right| <\epsilon$$ then...
  22. Mr Davis 97

    Proving "Limits of Finite Sequences Implies Limit of Sum

    Homework Statement For each ##n\in\mathbb{N}##, let the finite sequence ##\{b_{n,m}\}_{m=1}^n\subset(0,\infty)## be given. Assume, for each ##n\in\mathbb{N}##, that ##b_{n,1}+b_{n,2}+\cdots+b_{n,n}=1##. Show that ##\lim_{n\to\infty}( b_{n,1}\cdot a_1+b_{n,2}\cdot a_2+\cdots+b_{n,n}\cdot a_n) =...
  23. opus

    B Limits on Composite Functions- Appears DNE but has a limit

    Please see my attached image, which is a screenshot from Khan Academy on the limits of composite functions. I just want to check if I'm understanding this correctly, particularly for #1, which has work shown on the picture. Now my question: We are taking the limit of a composition of...
  24. alejandromeira

    B Time & Limit Velocity (Speed of Light)

    Hello. Today I've thinking about limit velocity and speed of ligth. We know that material particles can't achieve that speed, also when the speed of particles increases your own clock walks slowly. In the particular case of ligth your speed don't move anything. This it a explanation of why...
  25. opus

    Plotting Volume as a function of density, limit of this

    Homework Statement The density of an object is given by its mass divided by its volume: ##p=\frac{m}{V}## Use a calculator to plot the volume as a function of density (##V=\frac{m}{p}##), assuming a mass of 8kg (m=8). In the follow-up question (part b): Evaluate ##\lim_{p \rightarrow 0}...
  26. opus

    Why Does Splitting Limits Cause Problems with 0/0 Forms?

    Homework Statement Evaluate: $$\lim_{θ \rightarrow 0} {\frac{1-cos θ}{sin θ}}$$ Homework EquationsThe Attempt at a Solution By using trigonometric identities, I get to: $$\lim_{θ \rightarrow 0} {\frac{sin θ}{sin θ}}⋅\lim_{θ \rightarrow 0} {\frac{sin θ}{1+cos θ}}$$ By using the Limit Laws, I...
  27. karush

    MHB Value of $\displaystyle \lim_{x \to 0} g(x)$ Given Limit Statements

    $\textsf{find the value that $\displaystyle \lim_{x \to 0} g(x)$ must have if the given limit statements hold.}$ $$\displaystyle \lim_{x \to 0} \left(\frac{4-g(x)}{x} \right)=1$$ OK the only answer I saw by observation was 2 but the book says it is 4 not sure how you get it with steps
  28. opus

    B Limit of x & c as x→a: Basic Results

    In my text, it states the Basic Limit Results as follows: For any real number ##a##, and any constant ##c##, (i) ##\lim_{x \rightarrow a}{x}=a## (ii) ##\lim_{x \rightarrow a}{c}=c## Now from the previous chapter, I am used to seeing these as taking the limit of some function as the x values...
  29. opus

    A couple basic questions about finding a limit

    Homework Statement Find the following limit: $$\lim_{x \rightarrow 10}\frac{x-10}{4-\sqrt{x+6}}$$ Homework EquationsThe Attempt at a Solution [/B] Please see attached work. I have a few questions (other than if my solution is correct or not). First, is at step (ii)(C): What makes me uneasy...
  30. opus

    Finding a slope at a point on quadratic (intuition of limit)

    Homework Statement Find the slope of ##y=x^2+4## at (-2,8) and the equation for this line. Homework EquationsThe Attempt at a Solution This problem is intended to give an intuition on how limits work and I think I get the general idea. If we want to find the rate of change (or slope) of some...
  31. V

    Solving Limits: Finding a, b, c, and d for ∞-∞ Form

    Homework Statement lim x~∞ 〈√(x⁴+ax³+3x²+ bx+ 2) - √(x⁴+ 2x³- cx²+ 3x- d) 〉=4 then find a, b, c and d[/B]Homework Equations all the methods to find limits The Attempt at a Solution it can be said that the limit is of the form ∞-∞.I am completely stuck at this question.the answer is a=2...
  32. V

    What is the limit of the form 0/0?

    Homework Statement lim x~a 〈√(a⁺2x) -√(3x)〉 ÷ 〈√(3a+x) - 2√x〉[/B]Homework Equations rationalisation and factorisation[/B]The Attempt at a Solution i had done rationalisation but the form is not simplifying.pleasez help me.[/B]
  33. UFSJ

    Thermodynamic limit in Monte Carlo simulation

    Hi guys. I'm using the Monte Carlo method to simulate a spin lattice. If I have a square lattice, L x L, I can plot the phase transition temperature by the inverse of the lattice length (1/L) to find the phase transition temperature in the thermodynamic limit (extrapolating the curve for 1/L =...
  34. UFSJ

    I Extrapolating curve to thermodynamic limit for phase transit

    Hi guys. Anyone knows a article showing the method of extrapolation curve of the phase transition's temperature by the inverse of lattice size, applied at low-dimensional lattices, like nanotube and nanowire, for example? Thanks a lot!
  35. C

    Solve a limit with a nth root, with n -> infinity

    Homework Statement Solve the ##\lim_{n \rightarrow +\infty} \sqrt [n] \frac {n²+1} {n⁷-2} ## 3. The attempt of a solution: First I thought about using L'Hopital's rule, but the nth root makes it useless. Then I thought about to eliminate the root multiplying it by something that is one, but...
  36. Spinnor

    I Speed limit c in the multiverse

    Do we know enough of the workings of string theory to say what factors give rise to a large or small value of the velocity of propagation of massless fields for a given multiverse? Thanks!
  37. Scrope

    Solve Multi Var Limit: Help Appreciated!

    Homework Statement https://gyazo.com/268bef206850bfbf30fb0cca3f783599 <----- The question Homework EquationsThe Attempt at a Solution Had this on a test today, honestly not sure how to evaluate. I know you can pass the limit to the inside of arctan but I can't see how the inside goes to...
  38. Mr Davis 97

    I Indeterminate Limit: Evaluating ##\displaystyle \lim_{a \to 0^+} a^2 \log a##

    ##\displaystyle \lim_{a \to 0^+} a^2 \log a = 0 \cdot (- \infty)##, which is an indeterminate form. So ##\displaystyle \lim_{a \to 0^+} a^2 \log a = \lim_{a \to 0^+} \frac{\log a}{a^{-2}} = \lim_{a \to 0^+} \frac{\frac{1}{a}}{(-2)a^{-3}} = -\frac{1}{2}\lim_{a \to 0^+} a^2 = 0##. Is this correct?
  39. stevendaryl

    I Nonrelativistic limit of scalar field theory

    The Klein-Gordon equation has the Schrodinger equation as a nonrelativistic limit, in the following sense: Start with the Klein-Gordon equation (for a complex function ##\phi##) ## \partial_\mu \partial^\mu \phi + m^2 \phi = 0## Now, define a new function ##\psi## via: ##\psi = e^{i m t}...
  40. A

    Is there a limit to how steep the refractive index gradient can be

    Is there a limit to how steep a refractive index gradient can be before ray optics are no longer able to predict the path of the light? How is it related to wavelength? Under what conditions the light will be able to travel perpendicular to the gradient In a straight line? (having diffrent index...
  41. V

    MHB Does limit of "approximate zero set" converge to the zero set?

    Let f:\mathbb{R}^m\rightarrow\mathbb{R}^m. Define the zero set by \mathcal{Z}\triangleq\{x\in\mathbb{R}^m | f(x)=\mathbf{0}\} and an \epsilon-approximation of this set by \mathcal{Z}_\epsilon\triangleq\{x\in\mathbb{R}^m|~||f(x)||\leq\epsilon\} for some \epsilon>0. Clearly \mathcal{Z}\subseteq...
  42. M

    MHB Limit of Integral: Let u, A(x) be Functions

    Hey! :o Let $u(x,t), A(x)$ be functions, for which holds the following: We have the pde $u_t+a(u)u_x=0$. Let $A'(u)=a(u)$ then the pde can be written as $u_t+A(u)_x=0$. We have the following integrals $$\int_{a-\epsilon}^au\cdot \left (\frac{x-a}{\epsilon}+1\right )\...
  43. gibberingmouther

    I A rigorous definition of a limit and advanced calculus

    i'm trying to review calculus and look a little deeper into proofs/derivations/etc. I'm doing this both for fun and to review before i go back to school. am i the only one who has difficulty understanding the "rigorous" definition of the limit? i found this web page...
  44. MountEvariste

    MHB What is the Limit of the Hankel Determinant in a Matrix Challenge Problem?

    Challenge Problem: Let $A$ be an $r \times r$ matrix with distinct eigenvalues $λ_1, . . . , λ_r$. For $n \ge 0$, let $a(n)$ be the trace of $A^n$. Let $H(n)$ be the $r \times r$ the Hankel matrix with $(i, j)$ entry $a(i + j + n - 2)$. Show that $ \displaystyle \lim_{n \to \infty} \lvert...
  45. E

    Then, as ##b## goes to 0, can you find the limit of each factor separately?

    Homework Statement a. Compute the limit for f(x) as b goes to 0 Homework Equations $$f(x) = \frac{(a+bx)^{1-1/b}}{b-1}$$ ##a \in R##, ##b\in R##, ##x\in R## The Attempt at a Solution ##a+bx## goes to ##a## ##1/b## goes to ##\infty## so ##1-1/b## goes to ##-\infty## ##(a+bx)^{1-1/b}## then goes...
  46. itssilva

    A Gravitational binding energy and the TOV limit

    Disclaimer: to avoid giving the impression of speculative nature, I state the purpose of this thread is only to conflate known theory with my own understanding in a specific point and clarify where the disagreement lies; that is all. TOV limit: since early research in black hole (BH) formation...
  47. D

    I Tail in data of Duane-Hunt limit experiment

    https://photos-5.dropbox.com/t/2/AAC1PAsxThHE7dTxxumANssxIDSrZGA0wi9u1T2alieA9g/12/217355121/png/32x32/1/_/1/2/Screen%20Shot%202018-04-24%20at%2014.40.53.png/EJ6fyaMBGOQEIAIoAg/zVJasOZ8quUZpWc6eN6tzuO7YSmC-VjpQ4ikXIkpC8A?preserve_transparency=1&size=2048x1536&size_mode=3 So in looking at the...
  48. D

    I Limit of Extension: Can Function Have Different Limit?

    When we define a limit of a function at point c, we talk about an open interval. The question is, can it occur that function has a limit on a certain interval, but it's extension does not? To me it seems obvious that an extension will have the same limit at c, since there is already infinitely...
  49. EEristavi

    Continuity of Function - f(x)=|cos(x)|

    Homework Statement [/B] We have a function f(x) = |cos(x)|. It's written that it is piecewise continuous in its domain. I see that it's not "smooth" function, but why it is not continuous function - from the definition is should be..Homework Equations [/B] We say that a function f is...
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