Is (2X,5) Really an Ideal in Z[X]?

  • Context: Graduate 
  • Thread starter Thread starter Ad123q
  • Start date Start date
Click For Summary
SUMMARY

The discussion centers on the ideal (2X,5) in the polynomial ring Z[X]. It is established that (2X,5) is indeed an ideal, despite initial confusion regarding the absorbance property. The example provided demonstrates that elements like 5 + 2X and 7 + X can yield products that still belong to the ideal, as shown by the calculation (5 + 2X)(7 + X) = 2X^2 + 19X + 35. The key takeaway is that the presence of the constant term 5 allows for the inclusion of odd coefficients in the resulting polynomials, thus validating the ideal's structure.

PREREQUISITES
  • Understanding of polynomial rings, specifically Z[X]
  • Knowledge of ideal theory in abstract algebra
  • Familiarity with the absorbance property of ideals
  • Basic algebraic manipulation of polynomials
NEXT STEPS
  • Study the properties of ideals in polynomial rings, focusing on examples like (2X,5)
  • Learn about the concept of absorbance in the context of ring theory
  • Explore the implications of coefficients in polynomial multiplication
  • Investigate other types of ideals in Z[X] and their characteristics
USEFUL FOR

This discussion is beneficial for students and researchers in abstract algebra, particularly those studying polynomial rings and ideal theory. It is also useful for educators looking to clarify concepts related to ideals in Z[X].

Ad123q
Messages
19
Reaction score
0
I have in my notes that (2X,5) is an ideal of Z[X], but I can't see why this can be so.

For example 5+2X is in (2X,5) and 7+X is in Z[X] but then

(5+2X)(7+X) =
= 35+5X+14X+2X^2
= 2X^2+19X+35.

19 is not divisible by 2 and so this element is not in (2X,5), contradicting the "absorbance" property of ideals.
 
Physics news on Phys.org
Ad123q said:
I have in my notes that (2X,5) is an ideal of Z[X], but I can't see why this can be so.

For example 5+2X is in (2X,5) and 7+X is in Z[X] but then

(5+2X)(7+X) =
= 35+5X+14X+2X^2
= 2X^2+19X+35.

19 is not divisible by 2 and so this element is not in (2X,5), contradicting the "absorbance" property of ideals.



You seem to believe that any element in (2x,5) must have an even lineal coefficient, but this is wrong: the 5 there can multiply some x-coeff. of some

pol. and added to the even coefficient in the other factor we get an odd coef.

For example, the element 2x\cdot 1 + 5\cdot x = 7x belongs to the ideal...

DonAntonio
 

Similar threads

  • · Replies 6 ·
Replies
6
Views
2K
Replies
3
Views
3K
Replies
2
Views
2K
  • · Replies 6 ·
Replies
6
Views
3K
Replies
3
Views
1K
Replies
7
Views
2K
  • · Replies 15 ·
Replies
15
Views
2K
  • · Replies 9 ·
Replies
9
Views
3K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 3 ·
Replies
3
Views
8K