Complex numbers Watch

bubblegum21
Badges: 1
Rep:
?
#1
Report Thread starter 4 years ago
#1
I need to divide x^3 + 2x^2 + wx + u by x^2 - 2x where w= 4i + 2 and u=0. I don't know how to go about it. I know you're supposed to use long division but after that I'm lost. Any suggestions?
0
reply
davros
  • Study Helper
Badges: 16
Rep:
?
#2
Report 4 years ago
#2
(Original post by bubblegum21)
I need to divide x^3 + 2x^2 + wx + u by x^2 - 2x where w= 4i + 2 and u=0. I don't know how to go about it. I know you're supposed to use long division but after that I'm lost. Any suggestions?
If u = 0 then all your terms are divisible by x, so you can cancel that out to start with and just concentrate on dividing by x - 2.
0
reply
bubblegum21
Badges: 1
Rep:
?
#3
Report Thread starter 4 years ago
#3
(Original post by davros)
If u = 0 then all your terms are divisible by x, so you can cancel that out to start with and just concentrate on dividing by x - 2.
I forgot to mention that there's a +2 at the end of x^2-2x. Any suggestions?
0
reply
james22
Badges: 15
Rep:
?
#4
Report 4 years ago
#4
(Original post by bubblegum21)
I forgot to mention that there's a +2 at the end of x^2-2x. Any suggestions?
Use long division, not sure what the problem with that is.

What is the full question?
0
reply
bubblegum21
Badges: 1
Rep:
?
#5
Report Thread starter 4 years ago
#5
(Original post by james22)
Use long division, not sure what the problem with that is.

What is the full question?
Divide x^3 + 2x^2 + wx + u by x^2 -2x + 2 where w= -4i -2 and u=0. I am not sure how to use long division when complex numbers are involved
0
reply
james22
Badges: 15
Rep:
?
#6
Report 4 years ago
#6
(Original post by bubblegum21)
Divide x^3 + 2x^2 + wx + u by x^2 -2x + 2 where w= -4i -2 and u=0. I am not sure how to use long division when complex numbers are involved
Same as normal long division. It's no different.
0
reply
davros
  • Study Helper
Badges: 16
Rep:
?
#7
Report 4 years ago
#7
(Original post by bubblegum21)
Divide x^3 + 2x^2 + wx + u by x^2 -2x + 2 where w= -4i -2 and u=0. I am not sure how to use long division when complex numbers are involved
So let's be quite clear about this. The FULL question you've been asked is:

Divide x^3 + 2x^2 -(2 + 4i)x by x^2 - 2x + 2

Is there a reason why you introduced the unnecessary w and u? I'm just concerned we're missing the point of the question here
0
reply
bubblegum21
Badges: 1
Rep:
?
#8
Report Thread starter 4 years ago
#8
(Original post by davros)
So let's be quite clear about this. The FULL question you've been asked is:

Divide x^3 + 2x^2 -(2 + 4i)x by x^2 - 2x + 2

Is there a reason why you introduced the unnecessary w and u? I'm just concerned we're missing the point of the question here
thats correct. Well the first part of the question is to determine the values of w and u which I found by solving simultaneously. That bit is the second part
0
reply
james22
Badges: 15
Rep:
?
#9
Report 4 years ago
#9
(Original post by bubblegum21)
thats correct. Well the first part of the question is to determine the values of w and u which I found by solving simultaneously. That bit is the second part
Can you please post the full question still?
0
reply
davros
  • Study Helper
Badges: 16
Rep:
?
#10
Report 4 years ago
#10
(Original post by bubblegum21)
thats correct. Well the first part of the question is to determine the values of w and u which I found by solving simultaneously. That bit is the second part
As per james22, can we please see the full question so we know what the purpose behind the question is?
0
reply
bubblegum21
Badges: 1
Rep:
?
#11
Report Thread starter 4 years ago
#11
(Original post by james22)
Can you please post the full question still?
I have attached the question
Attached files
0
reply
james22
Badges: 15
Rep:
?
#12
Report 4 years ago
#12
(Original post by bubblegum21)
I have attached the question
What are you trying to use polynomial division on this?
0
reply
bubblegum21
Badges: 1
Rep:
?
#13
Report Thread starter 4 years ago
#13
(Original post by james22)
What are you trying to use polynomial division on this?
To find the other root. As 1+i is a root, so is it's conjugate 1-i. As it is a cubic root there is one other root left. So to find it we were taught to use polynomial division to f the last root
0
reply
davros
  • Study Helper
Badges: 16
Rep:
?
#14
Report 4 years ago
#14
(Original post by bubblegum21)
To find the other root. As 1+i is a root, so is it's conjugate 1-i. As it is a cubic root there is one other root left. So to find it we were taught to use polynomial division to f the last root
Given that you're told in part (a) that the coefficients are real, how have you ended up with an 'i' in your w???

This is why we asked to see the full question
0
reply
bubblegum21
Badges: 1
Rep:
?
#15
Report Thread starter 4 years ago
#15
(Original post by davros)
Given that you're told in part (a) that the coefficients are real, how have you ended up with an 'i' in your w???

This is why we asked to see the full question
Thats a fair point! As I got w= -4i-2, does the i just disappear and the answer is -6?
0
reply
james22
Badges: 15
Rep:
?
#16
Report 4 years ago
#16
(Original post by bubblegum21)
Thats a fair point! As I got w= -4i-2, does the i just disappear and the answer is -6?
No. It means you have gone wrong in your working.
0
reply
davros
  • Study Helper
Badges: 16
Rep:
?
#17
Report 4 years ago
#17
(Original post by bubblegum21)
Thats a fair point! As I got w= -4i-2, does the i just disappear and the answer is -6?
No it means you've got the wrong value for w!

(The point here is that from experience I know that it is highly unusual that you're going to be asked to divide a polynomial with complex terms by another polynomial with real terms. Therefore I felt that your original post had to be 'suspect' in some way )
0
reply
bubblegum21
Badges: 1
Rep:
?
#18
Report Thread starter 4 years ago
#18
(Original post by davros)
No it means you've got the wrong value for w!

(The point here is that from experience I know that it is highly unusual that you're going to be asked to divide a polynomial with complex terms by another polynomial with real terms. Therefore I felt that your original post had to be 'suspect' in some way )
I have recalculated and my w(-6) and u(8) satisfy the equation. Hopefully I'm on the right tracks now
0
reply
davros
  • Study Helper
Badges: 16
Rep:
?
#19
Report 4 years ago
#19
(Original post by bubblegum21)
I have recalculated and my w(-6) and u(8) satisfy the equation. Hopefully I'm on the right tracks now
Good stuff!!
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

University open days

  • Cranfield University
    Cranfield Forensic MSc Programme Open Day Postgraduate
    Thu, 25 Apr '19
  • University of the Arts London
    Open day: MA Footwear and MA Fashion Artefact Postgraduate
    Thu, 25 Apr '19
  • Cardiff Metropolitan University
    Undergraduate Open Day - Llandaff Campus Undergraduate
    Sat, 27 Apr '19

Have you registered to vote?

Yes! (124)
39.62%
No - but I will (17)
5.43%
No - I don't want to (20)
6.39%
No - I can't vote (<18, not in UK, etc) (152)
48.56%

Watched Threads

View All