Limit definition Definition and 58 Threads

I suppose that it is because we are in extended real numbers. But the definition of a limit when ##x_0 = \infty## and let's say ##L=\infty## is different. Why are these definitions equivalent? Isn't the key that ##U_{\varepsilon}(\infty)=\left(\frac {1}{\varepsilon},\infty\right)##?

Consider item ##vii##, which specifies the function ##f(x)=\sqrt{|x|}## with ##a=0## Case 1: ##\forall \epsilon: 0<\epsilon<1## $$\implies \epsilon^2<\epsilon<1$$ $$|x|<\epsilon^2\implies \sqrt{|x|}<\epsilon$$ Case 2: ##\forall \epsilon: 1\leq \epsilon < \infty## $$\epsilon\leq\epsilon^2...

I have the following definition: $$ \lim_{x\to p^+}f(x)=+\infty\iff \forall\,\,\varepsilon>0,\,\exists\,\,\delta>0,\,\,\text{with}\,\,p+\delta< b: p< x < p+\delta \implies f(x) > \varepsilon$$ From this, how can I get the definition of $$\lim_{x\to p^-}=-\infty? $$

I have the following definition: $$\lim_{x\to p^+}f(x)=+\infty\iff \forall\,\,\varepsilon>0,\,\exists\,\,\delta>0,\,\,\text{with}\,\,p+\delta< b: p< x < p+\delta \implies f(x) > \varepsilon$$ From this, how can I get the definition of $$\lim_{x\to p^-}=-\infty? $$

Hello everybody, could you help me with this problem please? I have to find a derivative in x0 of this function (without using L'Hospital's rule): I used the definition , but I don't know what to do next. Thank you.

<Moderator's note: Moved from a technical forum and thus no template.> $$\lim_{x \to 0} \cos(\pi/2\cos(x))/x^2$$ I tried to evaluate the limit this way, $$\lim_{x \to 0} \cos(\pi/2\cdot1)/x^2$$ since $$\cos0=1$$ $$\lim_{x \to 0} \cos(\pi/2\cdot1)/x^2=\lim_{x \to 0} 0/x^2$$ Now apply...

From Rosenlicht, Introduction to Analysis: Definition: Let E, E′ be metric spaces, let p0 be a cluster point of E, and let f(complement(p0)) be a function. A point q ∈ E" is called a limit of f at p0 if, given any e > 0, there exists a δ > 0 such that if p ∈ E , p < > p0 and d( p, p0) < δ...

Homework Statement Does the delta-epsilon limit definition in reverse work for describing limits in monotonic functions? By reversed, one means for lim (x -> a) f(x) = L if for each δ there corresponds ε such that 0 < | x-a | < δ whenever | f(x) - L | < ε. Homework EquationsThe Attempt at...

This is a simple exercise from Spivak and I would like to make sure that my proof is sufficient as the proof given by Spivak is much longer and more elaborate. Homework Statement Prove that \lim_{x\to a} f(x) = \lim_{h\to 0} f(a + h) Homework EquationsThe Attempt at a Solution By the...

in the limit definition of a sequence, why does epsilon has to be greater than 0 and not greater or equal to 0? thanks in advance.

Homework Statement Hey I'm trying to prove the rigorous definition of limit for the following function: Lim (x,y) approaches (1,1) of f(x,y)=(y*(x-1)^(4/3))/((x/1)^2+abs(x)*y^2) Homework Equations abs(x^2)<abs(x^2 +y^2) The Attempt at a Solution I know the rigorous definition of limit. I...

I am trying to explain to someone the formal notion of a limit of a function, however it has made me realize that I might have some faults in my own understanding. I will write down how I understand the subject and would very much appreciate if someone(s) can point out any...

Homework Statement Find the limit \lim_{(x,y)\to(2,2)}\frac{x^3-y^3}{x-y} Homework Equations \epsilon - \delta, baby: If the limit L exists, \forall \: \epsilon \: \exists \: \delta: 0 < \sqrt{(x-a)^2+(y-b)^2} < \delta \rightarrow |f(x,y)-L| < \epsilon The Attempt at a Solution By...

I am trying to find the derivative of x^x using the limit definition and am unable to follow what I have read. Can someone help me understand why lim [(x+h)^h -1]/h as h ---> 0 = ln(x). This part of the derivatio

Hello, I was just wondering, we have what could be called the indefinite derivative in the form of d/dx x^2=2x & evaluating at a particular x to get the definite derivative at that x. But with derivation, we can algebraically manipulate the limit definition of a derivative to actually evaluate...

Hi, Suppose you want to prove $|x - a||x + a| < \epsilon$ You know $|x - a| < (2|a| + 1)$ You need to prove $|x + a| < \frac{\epsilon}{2|a| + 1}$ So that $|x - a||x + a| < \epsilon$ Why does Michael Spivak do this: He says you have to prove --> $|x + a| < min(1, \frac{\epsilon}{2|a| +...

I think i discovered a new way to define an integral, i don't know if it helps in any particular case, but its an idea worth posting i think. The idea is to define the height of the rectangles based on one single point of the function and then build up the next heights for the other rectangles...

I've seen it written two different ways: $$\frac{\partial f}{\partial x} = \lim\limits_{h \rightarrow 0} \frac{f(x + h, y) - f(x,y)}{h}$$ and $$\frac{\partial f}{\partial x} = \lim\limits_{h \rightarrow 0} \frac{f(x_0 + h, y_0) - f(x_0,y_0)}{h}$$ where the latter evaluates the function at...

So there is something I don't understand in the definition of limit that is applied to some problem I have some intuition for like the rigorous limit definition but I don't have full understanding when applied to some problems. Use definition 2 to prove lim as z → i of z^2 = -1 The...

Application on the limit definition of "e" Hi, I have known that: (i) (1+\frac{a}{n})^n=((1+\frac{a}{n})^\frac{n}{a})^a\to e^a (ii) (1-\frac{1}{n})^n=(\frac{n-1}{n})^n=(\frac{1}{\frac{n}{n-1}})^{(n-1)+1}=(\frac{1}{1+\frac{1}{n-1}})^{(n-1)}\cdot (\frac{1}{1+\frac{1}{n-1}}) \to \frac{1}{e}\cdot...

Homework Statement Let f(x) =\begin{cases} 0 & \text{ if } x\leq 0 \\ e^\left ( -1/x \right ) & \text{ if } x> 0 \end{cases} Compute f'(x) for x < 0 and x > 0. Homework Equations f'(x) = \lim \ \ \ \ \ \ \displaystyle{\frac{e^{(-1/(x+h)} - e^{-1/x}}{h}} \\ \ \ \ \ \ \ \ \ \...

Homework Statement http://i.minus.com/jbicgHafqNzcvn.png Homework Equations The limit definition of a derivative: [f(x+h)-f(x)]/h as h approaches zero is f'(x) The Attempt at a Solution I'm just not understanding the wording of the question. The limit given in the question is...

Homework Statement http://i.minus.com/jbzvT5rTWybpEZ.png Homework Equations If a function is differentiable, the function is continuous. The contrapositive is also true. If a function is not continuous, then it is not differentiable. A function is differentiable when the limit definition...

Homework Statement Using the definition of derivative find f'(x) for f(x) = x - sqrt(x) Homework Equations None. The Attempt at a Solution lim h --> 0 : ((x + h) - sqrt(x + h) - x + sqrt(x))/h 1 - (sqrt(x + h) - sqrt(x))/h Multiply by conjugate.. 1 - h/(h*(sqrt(x) +...

Limit definition and "infinitely often" If we have a sequence of real numbers x_{n} converging to x, that means \forall \epsilon > 0, \exists N such that |x_n - x| < \epsilon, \forall n \geq N. So, can we say P (|x_n - x| < \epsilon \ i.o.) = 1 because for n \geq N, |x_n - x| < \epsilon...

Homework Statement It can be shown that lim n→∞(1 + 1/n)^n = e. Use this limit to evaluate the limit below. lim x→0+ (1 + x)^(1/x) Homework Equations The Attempt at a Solution So i guess what i need to do is try to get that limit in the form of the limit definition for e...

Homework Statement Prove lim x--> -1 1/(sqrt((x^2)+1) using epsilon, delta definition of a limit Homework Equations The Attempt at a Solution I know that the limit =(sqrt(2))/2 And my proof is like this so far. Let epsilon >0 be given. We need to find delta>0 s.t. if...

Homework Statement I'm reading through Taylor's advanced calculus and came across this question in section 7.2 : http://gyazo.com/6b0c5a2e4e605ff77bf6584eb3295948 Homework Equations The definition of the partial of f with respect to some variable at some point (a,b), let's say the...

If one uses the limit definition of a derivative (lim of (f(x)-f(a)) / (x-a)) as x approaches a) on a function and you get a value (ie. it is not undefined) does that mean the derivative of the function at that point exists? In other words, even if the limit definition of the derivative works...

Hi all ! I am terribly sorry if this was answered before but i couldn't find the post. So that's the deal. We all know that while x→∞ (1+1/x)^x → e But I am deeply telling myself that 1/x goes to 0 while x goes to infinity. 1+0 = 1 and we have 1^∞ which is undefined. But...

Trying to remember how to use the definition of a complex limit. \lim_{\Delta z\to 0}\frac{f(z+h)-f(z)}{\Delta z} f(z) = |z| = \sqrt{x^2+y^2} \Delta z = \Delta x + i\Delta y \lim_{\Delta x\to 0}\frac{\sqrt{(x+\Delta x)^2+(y+\Delta y)^2}- \sqrt{x^2+y^2}}{\Delta x} Is that correct? Or do I...

Homework Statement Sketch and label on the same pair of axes the graphs of y=f(x) and y=f'(x) for ... c) f(x)=2x Homework Equations The Attempt at a Solution f(x) = 2x f'(x) = lim as h→0 (2x+h-2x)/h = lim as h→0 (2x2h-2x)/h = lim as h→0 2x(2h-1)/h = lim as h→0 2x ∙ lim as h→0 (2h-1)/h = 2x...

\forall\epsilon\exists\delta[( (\epsilon\wedge\delta) > 0) \wedge ((| x - t| < \delta)\Rightarrow (|f(x) - f(t)|< \epsilon))] The part that seems wrong is the placement of the statement "delta is greater than zero" and "epsilon is greater than zero". It seems like these statements may need...

Homework Statement Guess the limit and use the \epsilon-\delta definition to prove that your guess is correct. \lim_{x \to 9}\frac{x+1}{x^2+1}2. The attempt at a solution Guess limit to be \frac{10}{82}=\frac{5}{41} Therefore: |\frac{x+1}{x^2+1}-\frac{5}{41}| =...

I know, I know, this topic has already been beat to death, but I'm still having a hard time understanding it despite having already read several forum threads and educational articles. Intuitively, the definition is stating that no matter how narrow we choose to make the "epsilon band"...

Homework Statement Here's the question...use the limit defintion to find the derivation of f(x) = x^2-4x Homework Equations does this use the defintion of the derivative formula (using Larson, et al 4th edition of Precaclulus graphing with limits...and trying to teach someone what to...

Homework Statement I had my second exam last week for my Calculus I course. I did alright, but we are supposed to correct them and bring them back for a quiz grade. However, I wasn't sure how to do this one on the test, and did not magically figure it out since then :) Find the derivative...

Limit definition gives a contradiction! say we are given sequences a(n), b(n) such that, a(n)->a, b(n)->b that means for epsilon>0, a-epsilon<a(n)<a+epsilon when n>N1 b-epsilon<b(n)<b+epsilon when n>N2 set N=max(N1,N2) when n>N...

Homework Statement I have been asked to find the derivative of f(x) = 0.39 + 0.24*floor(x-1) using the limit definition of a derivative. Is this possible? Homework Equations The Attempt at a Solution The limit as h approaches zero of 0.24(floor(x+h-1)-floor(x-1))/h is as far as...

Homework Statement Evaluate div v at P = (0, 0, 0) by actually evaluating (\int_S\mathbf{\hat{n}}\cdot \mathbf{v}\,dA)/V and taking the limit as B-->0. Take B to be the cube |x|\le\epsilon,|y|\le\epsilon,|z|\le\epsilon. Let \mathbf{v} = x\mathbf{\hat{i}} + 2y\mathbf{\hat{j}} -...

Hi. I'm a first-year calculus student and I'm fairly behind with my work. The transition is tough and when i read my textbook, I don't fully absorb everything. I thought I would post an example problem whose solution I do not follow completely, since it is fairly important in the scope of...

Homework Statement Prove that \lim_{x\rightarrow\ 0} (1+x)^{1/x}=e by an epsilon-delta proof. Homework Equations The Attempt at a Solution I did: x < a 1 + x < 1 + a but I couldn't go any further.

Homework Statement Find the derivative of f(x)=x1/3 using the limit definition of a derivative. Homework Equations The Attempt at a Solution I am stuck once I plug the numbers into the limit definition equation. How can I simplify the numerator in such a way the the h in the...

Homework Statement Use the limit definition of derivative to determine the derivative of the following function: f(x) = { sqrt(x^2+1) if x<=0 0 if x>0 Homework Equations I'm not sure as to why the function is not continuous at x=0, and so it's not differentiable at that...

Ues the limit definition to prove that the stated limit is correct. \lim_{x->-2} \frac{1}{x+1}=-1. The limit def' is |f(x)-L|<epsilon if 0<|x-a|< delta. So we have |\frac{1}{x+1} + 1| < \epsilon if 0 < |x- (-2)| < \delta \mbox{ therefore } |\frac{1}{x+1}||x+2| < \epslion \mbox{ if } 0 < |x +...

Homework Statement An example in the text that involves showing that x^2sin\frac{1}{x} approaches 0 as x approaches 0.Homework Equations \epsilon -\delta argumentThe Attempt at a Solution I can prove many limits efficiently now using \epsilon -\delta but I don't think I am that flexible with...

Homework Statement Obtain the first derivative of 10x by the limit definition.Homework Equations f'(x)=limh->0 f(x+h)-f(x)/hThe Attempt at a Solution f'(x)=limh->0 10x+h-10x/h I also know that h=1 as x approaches 0. Now, how do I make it so that you aren't dividing by h=0.

Homework Statement Use the limit definition to find the derivative of the function. f(x)= 1/(2x-4) Homework Equations f(x+h)-f(x)/h The Attempt at a Solution ok so first i plugged it all in.. (1/(2(x+h)-4))-(1/(2x-4)) / h from here i was going to do fly-by with the two top...

Hi, everyone- I have a quick question. When you solve for the derivative (as a linear transformation) using the limit definition of derivative, how does it go? For example, let p_k be defined as the projection function from Rn to R, projecting onto kth coordinate of the input value...

Homework Statement I'm trying to show that a sequence does not have a limit, so that would mean proving the negation of the limit definition is true, right? Is this a correct negation of the definition of what it means for a sequence to have a limit? Homework Equations The definition...