Polynomial Division (Cambridge O Level Additional Maths)

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Polynomial Division

What is polynomial division?

  • Polynomial division is the process of dividing two polynomials
    • This is usually only useful when the degree of the denominator is less than or equal to the degree of the numerator
  • Polynomial division is a method for splitting polynomials into factor pairs
    • (with or without a remainder term)

expressing a polynomial as a pair of factors

  • The main uses of polynomial division are
    • factorising polynomials
    • simplifying 'top-heavy' algebraic fractions

How do I divide polynomials?

  • The method used for polynomial division is just like the long division method for numbers
    • sometimes called the 'bus stop method'

numerical division example with bus stop method

  • The answer to a polynomial division question is built up term by term
    • Start by dividing by the highest power term
    • Write out this multiplied by the divisor and subtract

polynomial division example with bus stop method pt1

  •  Continue to divide by each reducing power term and subtracting your answer each time

polynomial division example with bus stop method pt2

  •  Continue until you are left with zero

polynomial division example with bus stop method pt3

  • If the divisor is not a factor of the polynomial then there will be a remainder term left at the end of the division

Worked example

For the polynomial straight f open parentheses x close parentheses space equals space x to the power of 4 plus 11 x squared minus 1divide straight f open parentheses x close parentheses by x space plus space 3 and write the remainder. 

Set up the polynomial division ('bus stop')

There is no x cubed term so write this as 0 x cubed in the method.
There is no x term so write this as 0 x in the method.

The first division step to consider is x to the power of 4 divided by x.

cie-add-maths-polynomial-division-we-solution-a-part-i

.Multiply x cubed by x plus 3 and subtract from x to the power of 4 space plus space 0 x.

cie-add-maths-polynomial-division-we-solution-a-part-ii

Bring the 11 x squared down and divide negative 3 x cubed by x. Continue with each step until you are finished.

cie-add-maths-polynomial-division-we-solution-a-part-iii

The remainder is 179.

Quadratic Divisor

What is meant by a quadratic divisor?

  • Polynomial division usually involves dividing by a linear term
    • a term of the form open parentheses x plus p close parentheses where p is a constant and usually an integer
  • It is possible to divide a polynomial by a quadratic term (and cubic, etc)
    • this would be a term of the form open parentheses x squared plus q x plus r close parentheses where q and r are constants
    • this is what is meant by a quadratic divisor

How do I divide by a quadratic divisor?

  • The process is the same as for a linear divisor
    • However, as x squared will not divide into x (in the polynomial division sense at least) the remainder, if there is one, could be of linear form, i.e. open parentheses r x plus s close parentheses where r and s are constants
      • It is possible that r equals 0 and so the remainder is still a constant

Examiner Tip

  • Give yourself plenty of room to do polynomial division
    • Not only will this help avoid errors, it will make your working clear
  • If you make a mistake and change something, fine, but if your method starts to get too messy it is best to restart

Worked example

Find the remainder when x to the power of 4 plus 4 x cubed minus x plus 1 is divided by x squared minus 2 x.

Set up the polynomial division ('bus stop') - there is no x squared term so write this as 0 x squared in the method.

The first division step to consider is x to the power of 4 divided by x squared.

bus stop method for polynomial division with a quadratic divisor

The remainder is bold 23 bold italic x bold plus bold 1.

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Roger

Author: Roger

Expertise: Maths

Roger's teaching experience stretches all the way back to 1992, and in that time he has taught students at all levels between Year 7 and university undergraduate. Having conducted and published postgraduate research into the mathematical theory behind quantum computing, he is more than confident in dealing with mathematics at any level the exam boards might throw at you.