Math 508: Advanced Analysis

Homework 10 - Bonus Problem
Lawrence Tyler Rush
<me@tylerlogic.com>
November 21, 2014
http://coursework.tylerlogic.com/courses/upenn/math508/homework10/bonusproblem

Solution:


B-1
B-2
Let C be the ring of continuous functions on [0,1].
a)
Let c [0,1] be fix. Define a φ : Cby
φ(f) = f (c)

Lemma 1. The function φ is a homomorphism.

Proof. The map φ preserves the operations of addition and multiplication due to

φ(f +g) = (f + g)(c) = f (c)+ g(c) = φ(f)+ φ (g)

and

φ(fg) = (fg)(c) = f (c)g(c) = φ(f)φ(g)

Furthermore the additive and multiplicative identities of C are mapped to the additive and multiplicative identities of :

φ(0) = (0)(c) = 0

and

φ(1) = (1)(c) = 1

__

With this definition of φ, we have that the kernel is exactly I = {f C | f(c) = 0}. Hence with the above lemma, I is an ideal of C. Futhermore, due to the above lemma and because φ is surjective (for a [0,1], the map x↦→a is mapped to a by φ), the Fundamental Theorem of Ring Homomorphisms implies that C∕I is isomorphic to since is a field, this implies that the ideal I is a maximal ideal.

b)