Divide using synthetic division $$ ( x^{3}-2x^{2}-31x-20 ) \div ( x-7 ) $$
Answer
The synthetic division table is:
$$ \begin{array}{c|rrrr}7&1&-2&-31&-20\\& & 7& 35& \color{black}{28} \\ \hline &\color{blue}{1}&\color{blue}{5}&\color{blue}{4}&\color{orangered}{8} \end{array} $$The solution is:
$$ \frac{ x^{3}-2x^{2}-31x-20 }{ x-7 } = \color{blue}{x^{2}+5x+4} ~+~ \frac{ \color{red}{ 8 } }{ x-7 } $$Explanation
Step 1 : Write down the coefficients of the dividend into division table. Put the zero from $ x -7 = 0 $ ( $ x = \color{blue}{ 7 } $ ) at the left.
$$ \begin{array}{c|rrrr}\color{blue}{7}&1&-2&-31&-20\\& & & & \\ \hline &&&& \end{array} $$Step 1 : Bring down the leading coefficient to the bottom row.
$$ \begin{array}{c|rrrr}7&\color{orangered}{ 1 }&-2&-31&-20\\& & & & \\ \hline &\color{orangered}{1}&&& \end{array} $$Step 2 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ 7 } \cdot \color{blue}{ 1 } = \color{blue}{ 7 } $.
$$ \begin{array}{c|rrrr}\color{blue}{7}&1&-2&-31&-20\\& & \color{blue}{7} & & \\ \hline &\color{blue}{1}&&& \end{array} $$Step 3 : Add down last column: $ \color{orangered}{ -2 } + \color{orangered}{ 7 } = \color{orangered}{ 5 } $
$$ \begin{array}{c|rrrr}7&1&\color{orangered}{ -2 }&-31&-20\\& & \color{orangered}{7} & & \\ \hline &1&\color{orangered}{5}&& \end{array} $$Step 4 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ 7 } \cdot \color{blue}{ 5 } = \color{blue}{ 35 } $.
$$ \begin{array}{c|rrrr}\color{blue}{7}&1&-2&-31&-20\\& & 7& \color{blue}{35} & \\ \hline &1&\color{blue}{5}&& \end{array} $$Step 5 : Add down last column: $ \color{orangered}{ -31 } + \color{orangered}{ 35 } = \color{orangered}{ 4 } $
$$ \begin{array}{c|rrrr}7&1&-2&\color{orangered}{ -31 }&-20\\& & 7& \color{orangered}{35} & \\ \hline &1&5&\color{orangered}{4}& \end{array} $$Step 6 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ 7 } \cdot \color{blue}{ 4 } = \color{blue}{ 28 } $.
$$ \begin{array}{c|rrrr}\color{blue}{7}&1&-2&-31&-20\\& & 7& 35& \color{blue}{28} \\ \hline &1&5&\color{blue}{4}& \end{array} $$Step 7 : Add down last column: $ \color{orangered}{ -20 } + \color{orangered}{ 28 } = \color{orangered}{ 8 } $
$$ \begin{array}{c|rrrr}7&1&-2&-31&\color{orangered}{ -20 }\\& & 7& 35& \color{orangered}{28} \\ \hline &\color{blue}{1}&\color{blue}{5}&\color{blue}{4}&\color{orangered}{8} \end{array} $$Bottom line represents the quotient $ \color{blue}{ x^{2}+5x+4 } $ with a remainder of $ \color{red}{ 8 } $.