Polynomial Division Homework: Q[x], Z5[x], R[x]

In summary, the conversation discusses dividing 2x5+x-1 by 3x2+1 in Q[x], Z5[x], and R[x]. The attempt at a solution involves using long division and fraction decomposition, with some confusion in Z5[x] due to not being able to use fractions. The final conclusion is that the division was done correctly, with confirmation through a check using (3x2+1)(4x3+2x) + 4x+4.
  • #1
sarah77
27
0

Homework Statement



Divide 2x5+x-1 by 3x2+1 in Q[x], Z5[x], and R[x]

The Attempt at a Solution



I believe the answer should be the same in Q[x] and R[x] and after division
I got 2/3x3-2/9x with remainder 1 2/9x-1. I had trouble in Z5 and would like someone to help me.
So far I have 3-1x3-1-1x but I do not think I am on the right track.

Please see attached work that I have completed so far..
 

Attachments

  • polynomial0001.pdf
    105.6 KB · Views: 195
Last edited:
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  • #2
I have attached the work I have done so far, please critique and help me finish. I am confused on what -3^-1x^3 becomes in Z5. Does it become 3x^3?
 
  • #3
Hmm, I don't think your long division was correct. What do you want to multiply 3x2 by to get the 2x5 term in Z5. Essentially, what times 3 equals 2? That should be the first step to that division.
 
  • #4
I have attached my work to this reply. Is this correct?
 

Attachments

  • division0001.pdf
    103.2 KB · Views: 185
  • #5
Has anyone been able to read my work and critique it? Please let me know if I am on the right track..
 
  • #6
[tex]\frac{2x^5}{3x^2}=\frac{2}{3}\,x^3\,,[/tex] not 4x3

Added in Edit:

Unless you're doing Z5[x], in which case it is 4x3, since 12 ≡ 2 mod 5 .
 
Last edited:
  • #7
How does 3 go into 4? Why couldn't you do a fraction decomposition?
 
  • #8
flyingpig said:
How does 3 go into 4? Why couldn't you do a fraction decomposition?

It is in Z5 so 3x4=12 which is 2 in Z5 or am I missing something?

I cannot use fractions, I don't think 2/3 is in Z5
 
  • #9
SammyS said:
[tex]\frac{2x^5}{3x^2}=\frac{2}{3}\,x^3\,,[/tex] not 4x3

It is in Z5, so I cannot use 2/3, it would be 3-1 and I tried that and it was incorrect..
 
  • #10
SammyS said:
[tex]\frac{2x^5}{3x^2}=\frac{2}{3}\,x^3\,,[/tex] not 4x3

Added in Edit:

Unless you're doing Z5[x], in which case it is 4x3, since 12 ≡ 2 mod 5 .

ok, so the division was correct then? All of it? Thank you for checking my work!
 
  • #11
sarah77 said:
It is in Z5 so 3x4=12 which is 2 in Z5 or am I missing something?

I cannot use fractions, I don't think 2/3 is in Z5

Right, I missed that your pdf was for Z5[x] .

It looks good.

Check by taking: (3x2+1)(4x3+2x) + 4x+4 .

It works out.
 
  • #12
Ok, thank you so much!
 

1. What is polynomial division?

Polynomial division is the process of dividing one polynomial by another polynomial in order to find the quotient and remainder.

2. What is Q[x] in polynomial division?

Q[x] is the set of all polynomials with coefficients from the rational numbers. It is often used in polynomial division to represent the coefficients of the quotient.

3. What is Z5[x] in polynomial division?

Z5[x] is the set of all polynomials with coefficients from the integers modulo 5. It is often used in polynomial division to represent the coefficients of the remainder.

4. What is R[x] in polynomial division?

R[x] is the set of all polynomials with coefficients from the real numbers. It is often used in polynomial division to represent the coefficients of both the quotient and remainder.

5. How is polynomial division used in real life?

Polynomial division is used in various fields of science and engineering, such as physics, computer science, and economics. It is used to model and solve real-world problems, such as predicting population growth or analyzing data sets.

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