Solving fourth degree polynomial

  • Context: Undergrad 
  • Thread starter Thread starter j-lee00
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    Degree Polynomial
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Discussion Overview

The discussion revolves around finding the solutions to the fourth degree polynomial equation (x^4)-(3x^3)-(3x^2)+2 = 0. Participants explore methods to find the remaining roots after two complex solutions are proposed, while addressing potential errors in the initial claims about these roots.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants propose that the two given solutions, x = 1 - i and x = 1 + i, can be used to find the remaining roots by dividing the polynomial by (x^2 - 2x + 2).
  • Others argue that the proposed solutions are incorrect, stating that substituting these values into the polynomial does not yield zero.
  • A later reply suggests that the original poster (OP) may have made a typo in the polynomial equation, as the roots provided do not satisfy the equation.

Areas of Agreement / Disagreement

There is disagreement regarding the validity of the proposed roots. Some participants assert that the roots are incorrect, while others initially accepted them without verification. The discussion remains unresolved regarding the correct roots of the polynomial.

Contextual Notes

Participants note that the discussion hinges on the accuracy of the initial polynomial equation and the proposed roots, which may have been miscommunicated. The mathematical steps to verify the roots are not fully explored.

Who May Find This Useful

Readers interested in polynomial equations, root-finding methods, and mathematical problem-solving may find this discussion relevant.

j-lee00
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Here it is

(x^4)-(3x^3)-(3x^2)+2 = 0

Two solutions are

x = 1 - i
x = 1 + i

How can i find the other solutions, (not graphically)

Thanks
 
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j-lee00 said:
Here it is

(x^4)-(3x^3)-(3x^2)+2 = 0

Two solutions are

x = 1 - i
x = 1 + i

How can i find the other solutions, (not graphically)

Thanks

General solution:
http://en.wikipedia.org/wiki/Quartic_equation

Numerical method:
http://en.wikipedia.org/wiki/Newton's_method
 
FrogPad said:
General solution:
http://en.wikipedia.org/wiki/Quartic_equation

Numerical method:
http://en.wikipedia.org/wiki/Newton's_method[/QUOTE]

There's no need for that. OP already has two of the roots so all that's required is to divide the original quartic by (x^2 - 2x + 2) and factorize the resultant quadratic.

BTW. (x^2 - 2x + 2) = (x-(1+i)) (x-(1-i))
 
Last edited by a moderator:
uart said:
There's no need for that. OP already has two of the roots so all that's required is to divide the original quartic by (x^2 - 2x + 2) and factorize the resultant quadratic.

BTW. (x^2 - 2x + 2) = (x-(1+i)) (x-(1-i))

good call.
 
One serious problem the OP has is that 1-i and 1+ i are NOT roots of
x4-3x3-3x2+2= 0!

If x= 1- i then x4-3x3-3x2+2= 4+ 12i and if x= 1+ i then x4-3x3-3x2+2= 4- 12i, not 0.
 
HallsofIvy said:
One serious problem the OP has is that 1-i and 1+ i are NOT roots of
x4-3x3-3x2+2= 0!

Oh yeah you're right. I just took his word for that and didn't check it.

My guess is that OP was given the two roots as part of the problem and has made a typo error in posting the equation.
 
yes sorry it was a typo but i got the method

thanks
 

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