Trouble with polynomial long division

In summary, the conversation discusses the long division solution of ##\frac 1 {1+y^2}## and the difficulty in duplicating the author's result. The conversation also includes a link to a forum post explaining the same process and a clarification on the use of deltas in the long division steps. The conclusion is to divide by ##1## instead of ##y^2##.
  • #1
SamRoss
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TL;DR Summary
Having trouble with a simple polynomial long division problem.
I'm reading a book where the author gives the long division solution of ##\frac 1 {1+y^2}## as ##1-y^2+y^4-y^6...##. I'm having trouble duplicating this result and even online calculators such as Symbolab are not helpful. Can anyone explain how to get it?
 
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  • #3
fresh_42 said:
It is difficult to display here and of course you can always multiply to check the result. I once explained it here:
https://www.physicsforums.com/threa...r-a-polynomial-over-z-z3.889140/#post-5595083Maybe this helps. It is the same as a normal division, step by step.

Thank you for your reply but I do not see how that link is related to my particular problem. Maybe it's because I'm not familiar with vocabulary like "splitting fields". Anyway, I have done basic polynomial long division before but never when the order of the dividend was less than the divisor. My thinking is to use negative exponents in the quotient but I don't think that would lead to the author's result.
 
  • #4
##1 : (1+y^2) = 1 \longrightarrow \Delta = -y^2##
##-y^2 : (1+y^2) = -y^2 \longrightarrow \Delta = y^4##
##y^4 : (1+y^2) = y^4 \longrightarrow \Delta = -y^6##
etc.

There is no restriction what has to be divided by what. In this case we start with ##1/1## and always divide by ##1##.
 
  • #5
fresh_42 said:
##1 : (1+y^2) = 1 \longrightarrow \Delta = -y^2##
##-y^2 : (1+y^2) = -y^2 \longrightarrow \Delta = y^4##
##y^4 : (1+y^2) = y^4 \longrightarrow \Delta = -y^6##
etc.

There is no restriction what has to be divided by what. In this case we start with ##1/1## and always divide by ##1##.

What is meant by ##1 \longrightarrow \Delta ## and all the other ## \longrightarrow \Delta ## steps?
 
  • #6
SamRoss said:
What is meant by ##1 \longrightarrow \Delta ## and all the other ## \longrightarrow \Delta ## steps?
That's what is more elaborated in the first example I gave you. The deltas are the differences, because long division is a sequence of subtractions.
##A:(1+y^2) = A \longrightarrow \Delta = -Ay^2## reads:
First divide ##A## by ##1## which yields the ##A## right of the equation sign.
Next we multiply ##(1+y^2)## with this ##A## which yields ##A+Ay^2##.
Now this has to be subtracted from what we have on the far most left: ##A- (A+Ay^2)= -Ay^2 =\Delta## which I wrote as ##\Delta##. It is our next far most left entry:
##-Ay^2 : (1-y^2)= -Ay^2 \longrightarrow \Delta = -Ay^2-(-Ay^2 \cdot (1+y^2))= -Ay^2 -(- Ay^2) -(- Ay^4) =Ay^4##
etc.

Finally we gather all intermediate results: ##A : (1+y^2) = A -Ay^2 + Ay^4 \mp \ldots##
 
  • #7
Got it. Thanks! I was dividing by ##y^2## instead of ##1##. I feel silly.
 

1. What is polynomial long division?

Polynomial long division is a method used to divide two polynomials, which are algebraic expressions made up of variables and coefficients. It is similar to long division with whole numbers, but instead of dividing numbers, we divide polynomials.

2. Why is polynomial long division important?

Polynomial long division is important because it allows us to simplify complex polynomial expressions and solve equations involving polynomials. It is also a necessary skill for many advanced mathematical concepts and real-world applications.

3. How do you perform polynomial long division?

To perform polynomial long division, we follow a set of steps:1. Arrange the terms of the dividend and divisor in descending order of their exponents.2. Divide the first term of the dividend by the first term of the divisor to get the first term of the quotient.3. Multiply the first term of the divisor by the first term of the quotient and subtract it from the dividend.4. Bring down the next term of the dividend and repeat the process until all terms have been brought down.5. The final result is the quotient, with any remainder written over the divisor.

4. What are some common mistakes made in polynomial long division?

Some common mistakes made in polynomial long division include:- Forgetting to bring down the next term of the dividend.- Making a mistake in the multiplication or subtraction step.- Dividing the wrong terms of the dividend and divisor.- Forgetting to include a placeholder for missing terms in the dividend.- Writing the final result in the wrong format.

5. How can I check my answer in polynomial long division?

You can check your answer in polynomial long division by multiplying the quotient and divisor and adding the remainder. The result should be equal to the dividend. If it is not, then there may be a mistake in your division process. You can also use a calculator to verify your answer.

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