# LONG DIVISION OF POLYNOMIALS

• PRACTICE (online exercises and printable worksheets)

In this section, hovering over any yellow-highlighted item will highlight a related term in the long division process;
moving away will ‘release’ the highlighting.
This should make it easier for you to connect written instructions to corresponding actions in the division problems.
(Try it by hovering here
and then moving away!)

## Long Division of Numbers

Think back to the long division of your grammar school days, say $\,1839\,$ divided by $\,7\,$:

 $\color{red}{\bf{2}}$ $\color{blue}{\bf{6}}$ $\color{purple}{\bf{2}}$ RECALL YOUR THOUGHT PROCESS: $7$ $1$ $8$ $3$ $9$ $7$ doesn't go into $1$;   it goes into $18$   two   times $-$ $1$ $4$ $2$ times $7$ is $14$;   subtract from previous row $4$ $3$ $9$ $8 - 4 = 4$;   bring down remaining digits;   $7$ goes into $43$   six   times $-$ $4$ $2$ $6$ times $7$ is $42$;   subtract from previous row $1$ $9$ $3 - 2 = 1$;   bring down remaining digit;   $7$ goes into $19$   two   times $-$ $1$ $4$ $2$ times $7$ is $14$;   subtract from previous row $5$ $9 - 4 = 5$ is less than the divisor (which is $7$), so stop the process and summarize results

How many times does $\,7\,$ go into $\,1839\,$?     $\,262\,$ times

How much is left over?     $\,5\,$

Notice that we stopped the process with the difference of  $\,5\,$ .
Thus, we never let  $\,7\,$  ‘go into’  $\,5\,$ .   So, $\,5\,$ still needs to be divided by $\,7\,$ !   So, here is one way to summarize the division problem: $$\frac{1839}{7} = 262 + \frac{5}{7}\qquad\qquad\qquad (\dagger)$$ Note:   the symbol ‘$\dagger$’ is read as ‘dagger’.
You will often see this dagger symbol used to label important information.

Equation $(\dagger)$ often appears in a different form, as shown below:

 $$\frac{1839}{7} = 262 + \frac{5}{7}$$ start with equation $(\dagger)$ $$7\left( \frac{1839}{7} \right) = 7(262) + 7(\frac 57)$$ multiply both sides by $\,7\,$ $\,1839\,$ $=$ $\,7\,$ $\cdot$ $\,262\,$ $+$ $\,5\,$ cancel extra factors of $\,1\,$ This is an equivalent way to summarize the division problem.

## Long Division of Polynomials

The long division of polynomials process is similar, with just a few extra considerations.

To illustrate, consider this division problem:   $\,\displaystyle\frac{x^3 - 8x + 2}{x+3}\,$
We want to know:

• How many times does   $\,x+3\,$   go into   $\,x^3 - 8x + 2\,$ ?
• How much is left over?

To begin:

• make sure that both the numerator and denominator are written in standard form,
with the highest power first and then descending powers
• put in zero terms for any missing powers:
for example, write   $\,x^3 - 8x + 2\,$   as   $\,x^3 \color{red}{+ 0x^2} - 8x + 2\,$
• for the ‘goes into’ process, ignore the $\,3\,$ in $\,x+3\,$;
that is, just say:   ‘How many times does $\ x\$ go into ... ?’
• in ‘the thought process’ below,
hover over each highlighted term to locate the corresponding term in the division problem

 $\color{red}{x^2}$ $\color{blue}{-\quad 3x}$ $\color{purple}{+\quad 1}$ THE THOUGHT PROCESS: $x$ $+\quad 3$ $x^3$ $+$ $0x^2$ $-$ $8x$ $+$ $2$ $\,x\,$ goes into $\,x^3\,$ how many times?   $\displaystyle\frac{x^3}{x} =$ $\color{red}{x^2}$ $\color{green}{\bf{-}}$ $\color{green}{\bf{(}}$ $x^3$ $+$ $3x^2$ $\color{green}{\bf{)}}$ $x^2$ $(x+3)$ $=$ $x^3 + 3x^2\$;   subtract from previous row (put parentheses and minus sign) $-3x^2$ $-$ $8x$ $+$ $2$ $0x^2 - 3x^2 = -3x^2$;   bring down remaining terms ; $x$ goes into $\,-3x^2\,$ how many times? $\displaystyle\frac{-3x^2}{x} =$ $\color{blue}{-3x}$ $\color{green}{\bf{-}}$ $\color{green}{\bf{(}}$ $-3x^2$ $-$ $9x$ $\color{green}{\bf{)}}$ $-3x(x+3) = -3x^2 - 9x\$;   subtract from previous row (put parentheses and minus sign) $x$ $+$ $2$ $-8x - (-9x) = x\$;   bring down remaining term; $x\,$ goes into $x\,$ how many times?   $\displaystyle\frac{x}{x} =$ $\color{purple}{1}$ $\color{green}{\bf{-}}$ $\color{green}{\bf{(}}$ $x$ $+$ $3$ $\color{green}{\bf{)}}$ $1(x+3) = x + 3\$; subtract from previous row (put parentheses and minus sign) $-1$ $2 - 3 = -1\$; the degree of $\,-1\,$ is less than the degree of $\,x+3\,$, so stop the process and summarize results

How many times does $\,x+3\,$ go into $\,x^3 - 8x + 2\,$?     $\,x^2 - 3x + 1\,$ times

How much is left over?     $\,-1\,$
Thus:

$\displaystyle\frac{x^3 - 8x + 2}{x+3} = x^2 - 3x + 1 + \frac{(-1)}{x+3}$       or, equivalently,       $\,x^3 - 8x + 2\,$ $=$ $\,(x+3)\,$ $\,(x^2 - 3x + 1)\,$ $+$ $\,(-1)\,$

## Using Web-Based Technology for Long Division of Polynomials

Of course, WolframAlpha can do division of polynomials!   The widget below computes   $\displaystyle\frac{\text{numerator}}{\text{denominator}}$  .
Type in any numerator and denominator that you want, and then press ‘Submit’.
Have fun!