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Synthetic Division

  1. Nov 14, 2016 #1
    1. The problem statement, all variables and given/known data

    So I thought I knew how to do synthetic division but ran into this problem

    [tex] 4a^4+4a^3-9a^2-4a+16 / (a^2-2) [/tex]

    2. Relevant equations


    3. The attempt at a solution

    All the examples I can find don't have a second degree polynomial in the denominator. i.e. they are a-3 or a+2. How do you go about doing this division with higher order polynomials in the denominator?

    Like do I still set it up as ?

    -2 | 4 4 -9 -4 16
    Thanks
     
  2. jcsd
  3. Nov 14, 2016 #2

    fresh_42

    Staff: Mentor

    Here's an example I recently wrote here:
    https://www.physicsforums.com/threa...r-a-polynomial-over-z-z3.889140/#post-5595083

    It is basically the exact same thing as with numbers. As a hint: as long as it's new to you, proceed step by step and watch out not to mess up the signs.

    Edit: Of course your example starts with ##4a^4 : (a^2-2) = 4a^2 + ... ## and then the subtraction of ##4a^2 \cdot (a^2-2)= 4a^4-8a^2##
     
  4. Nov 14, 2016 #3

    Mark44

    Staff: Mentor

    As far as I know, synthetic division can be performed only when the divisor is a first degree polynomial whose leading coefficient is 1. IOW, the divisor has to be x - a, with a being either positive or negative.

    The work that @fresh_42 showed is polynomial long division. Synthetic division is a special case of polynomial long division.
     
  5. Nov 15, 2016 #4

    SammyS

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    I suppose you mean
    ##\ (4a^4+4a^3-9a^2-4a+16) / (a^2-2) ##
    If that were division by ##\ a - 2\,,\ ## then you would have positive 2 out front in your set-up for synthetic division.

    But yes, you can do some form of synthetic division here. The divisor only has terms of even degree, so it interacts with the even degree terms independently from the odd degree terms.

    You can look at this as ##\displaystyle \ \frac{4a^4-9a^2+16}{a^2-2} + a\frac{4a^2-4}{a^2-2} \,.##

    Do two individual synthetic divisions.
     
  6. Nov 19, 2016 #5

    lurflurf

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    Homework Helper

    $$

    \begin{array}{rr|rrrrr}
    & & 4&4 & -9 & -4 & 16 \\
    \hline
    & 2 & & & 8 & *&*&%8 &-2
    \\
    0 & & & 0&*&*&%0 & 0 &
    \\
    \hline

    &&4&*&*&*&*&%{4}&-1& 4&14
    \end{array}

    $$

    The numbers to the left multiply the bottom left numbers to yield the middle numbers
    top and middle numbers add to give bottom numbers
    try to fill in the rest
     
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