Closed Definition and 1000 Threads

Let a and b be real numbers with a<b, and let x be a real number. Suppose that for each ε>0, the number x belongs to the open interval (a-ε, b+ε). Prove that x belongs to the interval [a, b].

I was busy doodling and basically ended up constructing this differential equation: p'(t)=c(t)p(t)-c(t-T)p(t-T) Obviously I've dealt with eq's like p'(t)=c(t)p(t) but I'm getting stuck because of the second term. Does this differential equation even have a closed form? Thanks.

Hi, If X \LARGE is a metric space and E \subset X is a discrete set then is E \LARGE open or closed or both? Here's my understanding: E \LARGE is closed relative to X \LARGE. proof: If p \subset E then by definition p \LARGE is an isolated point of E \LARGE, which implies that p...

Hello. Does anybody happen to know a closed form of this infinitely nested radical? http://imageshack.us/a/img268/6544/radicals.jpg By any chance, maybe you even saw it somewhere? I haven't had too much success so far. At the moment I am so desperate that I'm even willing to try and...

Doing a T-s and P-v diagram from a real power plant Rankine cycle. The cycle, after the condenser, goes through one pump, and then in series: gland steam condenser 4 closed feedwater heaters 1 open feedwater heater another pump 2 closed feedwater heater boiler Temperature and...

Main question in the title. I did a group work in analytic mechanics about pendulum in rotating reference frame and stumbled upon this one: http://peer.ccsd.cnrs.fr/docs/00/50/17/84/PDF/PEER_stage2_10.1016%252Fj.ijnonlinmec.2008.03.009.pdf. Does this always hold? In my solution, there are two...

A team including Anton Zeilinger has performed an experiment closing the so-called "fair sampling loophole" for photons. http://arxiv.org/abs/1212.0533 Bell violation with entangled photons, free of the fair-sampling assumption Marissa Giustina, Alexandra Mech, Sven Ramelow, Bernhard...

If we assumed an empty space, but also assumed space dimensions are closed ( repeat after some distance D ), what would the metric tensor look like? Is this just equivalent to a space with a constant curvature R? If so, how does R relate to D? Would the time dimension also necessarily be...

Homework Statement show the set {f: ∫f(t)dt>1(integration from 0 to 1) } is an open set in the metric space ( C[0,1],||.||∞） and if A is the subset of C[0,1] defined by A={f:0<=f<=1} is closed in the norm ||.||∞ norm. Homework Equations C[0,1] is f is continuous from 0 to 1.and ||.||∞...

Ok, so I am currently building a cloud chamber for a major presentation in the area of Thermodynamics (or Energy and Temperature) and I've been thinking quite a bit about this theory...and i could be wrong...so don't tell me off about it... So the general physics of a cloud chamber, Isopropyl...

Homework Statement The closed loop is vertical and the magnetic field is a north and south pole such that the looped end faces the magnetic poles. A multiple choice question answer stated that the closed loop will have a smaller acceleration than 10mls ^2 as it would experience an...

So this is more so a general question and not a specific problem. What exactly is the diefference between closed and boundedness? So the definition of closed is a set that contains its interior and boundary points, and the definition of bounded is if all the numbers say in a sequence are...

This may seem like a silly question, but I'll ask it anyways. :) In the Munkres text, he proves this by showing that one-point sets are closed, which I completely understand why it follows that finite point sets are closed. He does so by showing that the arbitrary one-point set {x0} equals...

Given \epsilon > 0 , suppose \omega_f(x) < \epsilon for each x \in [a,b] . Then show there is \delta > 0 such that for every closed interval I \in [a,b] with l(I)< \delta we have \omega_f(I) < \epsilon . My first approach to this was trying to think of it as an anaglous to the definition...

Let ρ(x) be a continuous function on ℝ, which evaluates ρ(x)=0 when |x|≥1 and that meets following. ∫[-1,1]ρ(x)dx=1 And let ψ(x) be a continuous function on interval [-1,1], prove lim[n→∞] n∫[-1,1]ρ(nx)ψ(x)dx = ψ(0). is denoted. This is NOT a homework but a past exam problem of...

Does entropy in a closed system always increase OR remain constant ( in equilibrium ). I have a friend arguing it is ALWAYS increasing. His latest argument was, "if no energy enters or leaves an isolated system, the availability of the remaining energy decreases."

Homework Statement One kg of air is heated in a closed rigid vessel such its temperature changes from 27 C to 427 C . Find the heat transfered and change in internal energy . Assume : - R= 0.287 KJ/kg k Cv = 0786 KJ/Kg k Homework Equations Q = mXCX(T2 - T1 ) The Attempt at a...

Homework Statement Ok so I have been given a diagram which if it worked should be attached. I am having a fair bit of trouble understanding it. Now I am aware that there is both electrical and conventional currents but I am confused as to whether this is electrical or conventional. I have been...

1. {(x,y)\in R^2 such that 2x+y<=2, x-y>4} Determine whether this subset of R^2 is open, closed or neither open nor closed. 2. I think this is an open subset but not sure how to prove it. I have rearranged the equations to give x>2, y<=-2x+1, y< x-1. I think it is open because x can get...

Hi guys, I would like to understand why a circle (and in general a n-sphere) as a subset of R^2 (in general R^(n+1)) with the standard topolgy is considered a closed and a bounded set. I think that this can be a closed set because its complement (the interior of the circle and the rest of...

Homework Statement Given binary string of length n. substrings of 1's should be even. (given 0 is a delimeter) eg) 10111 is broken down into 1 and 111 (all odd) so, for example string with H(n = 4) 0000 1100 0110 0011 1111 there are 5 of them. H(n = 3) 000 110 011 there are 3 of...

HI! I was wandering if there is a proof that the harmonic sum \sum\frac{1}{k} has no closed form. Something like the proof that an equation with degree more than 4 has no solution in terms of radicals.

Hello everyone! I want to show that all countable sets are closed. I can show that finite sets are closed, and the set of all natural numbers is closed by showing its complement to be a union of open sets. Now, can I start like this: A is a countable set. Every element in A can be "mapped" to...

Homework Statement http://i.imgur.com/69BmR.jpg Homework Equations The Attempt at a Solution a, c are right because f(c) is continuous. b, d are right because f'(c) is differentiable over the interval I am not sure about e. Can anyone explain to me?

Homework Statement Basically, prove the Extreme Value Theorem. "If f is a continuous function over the interval [a,b] then f reaches a max and a min on that interval." Homework Equations In this case they're more like definitions and things I have proved so far. Intervals are...

http://imageshack.us/a/img141/4963/92113198.jpg hey, I'm having some trouble with this question, For part a) I know that in order for c_0 to be closed every sequence in c_0 must converge to a limit in c_0 but I am having trouble actually showing that formally with the use of the norm...

This is just a quick question about sets that include plus or minus infinity on the extended real line. I am wondering about this in regards to measure in analysis so specifically, is [-∞,a) open or closed? I hadn't seen the extended reals before this class and we really didn't spend anytime...

A closed vessel full of water is rotating with constant angular velocity \Omega about a horizontal axis. Show that the surfaces of equal pressure are circular cylinders whose common axis is at a height g/{\Omega}^2 above the axis of rotation. Any ideas? I do not know how to start.

Hi all, is sample space an open set or a closed set? Thanks in advance

Good day! Im currently reading the book of Steven R. Lay's "Analysis with an Introduction to Proof, 3rd ed.". According to his book, if a subset S of ℝ contains all of its boundary then it is closed. But i find this wrong since if we consider S={xεQ;0≤x≤2}, then it can be shown that S...

Dewing of a mirror or object glass can be countered with various devices and methods, but its occurrence inside a closed system is particularly problematic. I have received the following enquiry (from an experienced observer who has used several instruments over many years) concerning...

The eigenvalues are found by $$ \tan\lambda_n = \frac{1}{\lambda_n} $$ For large eigenvalues, the intersection get closer and closer to $\lambda_n = \pi k$ where $k\in\mathbb{Z}^+$ and $k > 15$. Is this correct? Without arbitrary picking a $k$, is there a better way to determine a $k$ for when...

Hello, I have a few questions regarding machine tool drive and feed back system. Say I have a 1 meter long guide way and a carriage that is driven by DC motor. This carriage glides on air bearings. The drive mechanism has pinch rollers that pinch a drive rod and these rollers are driven by...

Homework Statement I need to prove that a closed ball(radius r about x0) is closed and bounded. The same goes for a sphere(radius r about x0). Homework Equations The Attempt at a Solution How does one go about proving something is closed and bounded? My book is not very helpful...

Homework Statement Determine each of the following sets as open, closed, neither or both. a) {1/n : n \in N } b) N c) Q d) \bigcap^{∞}_{n=1}(0,1/n) e) {x: |x-5|\leq 1/2 f) {x: x^2>0} Homework Equations Open sets are sets that do not contain their boundary points. Closed sets contain...

Spivak's proof of "A closed bounded subset of R^n is compact" Hi guys, I'm currently taking a differential geometry course and decided I would read Spivak's Calculus on Manifolds, and then move on to his Differential Geometry series. There's a proof in here that feels unjustified to me, so...

Closed and open at the same time??! I am doing a reading course with a professor using Rudin's Real and Complex Analysis. I had never seen any topology before so the professor told me to work through the first two chapters of Hocking's Topology. I am taking my sweet time with it because I...

Prove that every closed set in $\mathbb{R}$ is the intersection of a countable collection of open sets. Let $G_n$ be a countable collection of open sets. Then we would have 2 cases either $x\in\bigcap G_n$ which is a point which is closed. Or we could $(a,b)$ in all $G_n$ but how to show that...

Homework Statement This question has two parts : (a) Let F be a finite collection of closed sets in ℝn. Prove that UF ( The union of the sets in F ) is always a closed set in ℝn. (b) Let F be a finite collection of closed intervals An = [\frac{1}{n}, 1- \frac{1}{n}] in ℝ for n =...

Homework Statement a fluid undergoes a reversible adiabatic compression from .5 MPa, .2 m3 to .05 m3 according to the law PV1.3 = constant. determine the change in enthalpy, internal energy and work transfer during the process. Homework Equations P1V11.3 = P2V21.3 dH = T dS + V dP dS = 0...

Homework Statement Let M be a metric space and A\subseteqM be any subset: Prove that if A is contained in some closed ball, then A is bounded. Homework Equations Def of closed-ball: \bar{B}R(x) = {y\inM:d(x,y)≤R} for some R>0 Def of bounded: A is bounded if \existsR>0 s.t. d(x,y)≤R...

Prove that the following are equivalent: a) A is bounded, b) A is "in" a closed ball Homework Statement The full problem is: Let M be a metric space an A\subseteqM be any subset. Prove that the following are equivalent: a)A is bounded. b)A is contained in some closed ball c)A is contained in...

How does Gauss's divergence law work in a closed finite universe? Let's say the universe were a 4-sphere, with a single electron. How can I work out the field of the electron? If I draw a 3-sphere around the electron, then I split space into two regions. One region contains an electron, so...

Homework Statement A closed tube resonates at 440 Hz when it is 0.195 m long and 0.586 m long. Determine the speed of sound. How do I do this? Homework Equations wavelength=4L v=fw The Attempt at a Solution v= 440 (4L) I'm just not sure how to use both lengths given, can someone...

Could you please give me a hint on how to show that a set of operators with a property P is closed under addition? In other words, how one could prove that a sum of any two operators from the set still possesses this property P. The set is assumed to be infinite. Any references, comments...

If we define a set, c, to be R^2, how is it open and closed? The definitions I'm using: Open set: Open set, O, is an open set if for all points x are in O, and we can find ONE B(x,ρ) such that B(x,ρ) is less than zero. Closed set: Compliment of an open set, AKA R^n/O. This isn't a HW...

If not, does the second law of thermodynamics even apply? What role would entropy play if it is not?

I'm looking at Rao: Topology, Proposition 1.5.4, "A closed subspace of a Lindelöf space is Lindelöf." He gives a proof, which seems clear enough, using the idea that for each open cover of the subspace, there is an open cover of the superspace. But I can't yet see where he uses the fact that the...

Proving a Set is Closed (Topology) Homework Statement Let Y be an ordered set in the order topology with f,g:X\rightarrow Y continuous. Show that the set A = \{x:f(x)\leq g(x)\} is closed in X. Homework Equations The Attempt at a Solution I cannot for the life of me figure...

Hi, I was reading over a solution after working on a problem and got confused about some parts: http://nweb.math.berkeley.edu/sites/default/files/pages/f10solutions.pdf (first problem) First, how do we know that there are disjoint open sets U and V for each of the separated sets? (does...