Let R[:] be the set of all expressions a = ao+ajx+a2x² + …=La;x i=0 where a¡ e R for all nonnegative integers i. Informally, an element of R[t] is like a polynomial except that it can have infinitely many terms. (a) Carefully write down definitions of addition and multiplication operations for R[[:], analogous to the definitions for R[x] in the notes. Given a,b E R[:], your defi- nitions should indicate what each coefficient of the sum a + b and product ab is. (b) Let f = ao+ax+.+a„x" be a polynomial. I can treat f as an element of R[t] by defining a,+1,an+2,….. all to equal 0. This shows that R[x] C R[t]. If you had already proved that R[x]] was a ring, how could you use this fact to help you prove R[x] is a ring? (c) Let a E R[l]] with ao # 0. Prove that a has a multiplicative inverse in R[[x]. You may assume that the multiplicative identity element in R[x] is IR] = 1+0x+ 0x²+0x³ + •…·, and that multiplication in R[x] is commutative. [Hint. If ab = 1R1], equate coefficients and solve for bo, bị, b3, …. in turn.]
Let R[:] be the set of all expressions a = ao+ajx+a2x² + …=La;x i=0 where a¡ e R for all nonnegative integers i. Informally, an element of R[t] is like a polynomial except that it can have infinitely many terms. (a) Carefully write down definitions of addition and multiplication operations for R[[:], analogous to the definitions for R[x] in the notes. Given a,b E R[:], your defi- nitions should indicate what each coefficient of the sum a + b and product ab is. (b) Let f = ao+ax+.+a„x" be a polynomial. I can treat f as an element of R[t] by defining a,+1,an+2,….. all to equal 0. This shows that R[x] C R[t]. If you had already proved that R[x]] was a ring, how could you use this fact to help you prove R[x] is a ring? (c) Let a E R[l]] with ao # 0. Prove that a has a multiplicative inverse in R[[x]. You may assume that the multiplicative identity element in R[x] is IR] = 1+0x+ 0x²+0x³ + •…·, and that multiplication in R[x] is commutative. [Hint. If ab = 1R1], equate coefficients and solve for bo, bị, b3, …. in turn.]
Elements Of Modern Algebra
8th Edition
ISBN:9781285463230
Author:Gilbert, Linda, Jimmie
Publisher:Gilbert, Linda, Jimmie
Chapter1: Fundamentals
Section1.7: Relations
Problem 21E: 21. A relation on a nonempty set is called irreflexive if for all. Which of the relations in...
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