Question

In: Advanced Math

Let x = inf E. Prove that x is an element of the boundary of E....

Let x = inf E. Prove that x is an element of the boundary of E. Here R is regarded as a metric space with d(p,q) = |q−p| for p,q ∈R

Expert Solution

Defination : A point is said to be an boundary point of if every neighbourhood of contains a point of as well as a point of

Given ,

We will prove by contradiction that is an boundary point of

If is not an boundary point of then every neighbourhood of contains a point of as well as a point of ia not true .

There exist a neighbourhood of say such that

As is a neighbourhood of so there exist a such that

Now as and

which is a contradiction to because if then all other elements of should be greater than or equals to x .

So our assumption is not an boundary point of is wrong .

Hence is an boundary point of .

.

If you have any doubt or need more clarification at any step please comment .

Colby Messinger answered 2 years ago

Let (xn), (yn) be bounded sequences. a) Prove that lim inf xn + lim inf yn...

Let (xn), (yn) be bounded sequences. a) Prove that lim inf xn + lim inf yn ≤ lim inf(xn + yn) ≤ lim sup(xn + yn) ≤ lim sup xn + lim sup yn. Give example where all inequalities are strict. b)Let (zn) be the sequence defined recursively by z1 = z2 = 1, zn+2 = √ zn+1 + √ zn, n = 1, 2, . . . . Prove that (zn) is convergent and find its limit. Hint; argue...

let D be an integral domain. prove that an element of D[x] is a unit if...

let D be an integral domain. prove that an element of D[x] is a unit if an only if it is a unit in D.

Let G be connected, and let e be an edge of G. Prove that e is...

Let G be connected, and let e be an edge of G. Prove that e is a bridge if and only if it is in every spanning tree of G.

Let (xn) be a sequence with positive terms. (a) Prove the following: lim inf xn+1/ xn...

Let (xn) be a sequence with positive terms. (a) Prove the following: lim inf xn+1/ xn ≤ lim inf n√ xn ≤ lim sup n√xn ≤ lim sup xn+1/ xn . (b) Give example of (xn) where all above inequalities are strict. Hint; you may consider the following sequence xn = 2n if n even and xn = 1 if n odd.

Let G be a cyclic group generated by an element a. a) Prove that if an...

Let G be a cyclic group generated by an element a. a) Prove that if an = e for some n ∈ Z, then G is finite. b) Prove that if G is an infinite cyclic group then it contains no nontrivial finite subgroups. (Hint: use part (a))

1. Prove that the Cantor set contains no intervals. 2. Prove: If x is an element...

1. Prove that the Cantor set contains no intervals. 2. Prove: If x is an element of the Cantor set, then there is a sequence Xn of elements from the Cantor set converging to x.

(a) Let <X, d> be a metric space and E ⊆ X. Show that E is...

(a) Let <X, d> be a metric space and E ⊆ X. Show that E is connected iff for all p, q ∈ E, there is a connected A ⊆ E with p, q ∈ E. b) Prove that every line segment between two points in R^k is connected, that is Ep,q = {tp + (1 − t)q | t ∈ [0, 1]} for any p not equal to q in R^k. C). Prove that every convex subset of R^k...

Q2. Let (E, d) be a metric space, and let x ∈ E. We say that...

Q2. Let (E, d) be a metric space, and let x ∈ E. We say that x is isolated if the set {x} is open in E. (a) Suppose that there exists r > 0 such that Br(x) contains only finitely many points. Prove that x is isolated. (b) Let E be any set, and define a metric d on E by setting d(x, y) = 0 if x = y, and d(x, y) = 1 if x and y...

Let u(x, y) be the harmonic function in the unit disk with the boundary values u(x,...

Let u(x, y) be the harmonic function in the unit disk with the boundary values u(x, y) = x^2 on {x^2 + y^2 = 1}. Find its Rayleigh–Ritz approximation of the form x^2 +C1*(1−x^2 −y^2).

. Let x, y ∈ R \ {0}. Prove that if x < x^(−1) < y...

. Let x, y ∈ R \ {0}. Prove that if x < x^(−1) < y < y^(−1) then x < −1.