Divide using synthetic division $$ ( x^{3}-3x^{2}-9x-5 ) \div ( x-1 ) $$
Answer
The synthetic division table is:
$$ \begin{array}{c|rrrr}1&1&-3&-9&-5\\& & 1& -2& \color{black}{-11} \\ \hline &\color{blue}{1}&\color{blue}{-2}&\color{blue}{-11}&\color{orangered}{-16} \end{array} $$The solution is:
$$ \frac{ x^{3}-3x^{2}-9x-5 }{ x-1 } = \color{blue}{x^{2}-2x-11} \color{red}{~-~} \frac{ \color{red}{ 16 } }{ x-1 } $$Explanation
Step 1 : Write down the coefficients of the dividend into division table. Put the zero from $ x -1 = 0 $ ( $ x = \color{blue}{ 1 } $ ) at the left.
$$ \begin{array}{c|rrrr}\color{blue}{1}&1&-3&-9&-5\\& & & & \\ \hline &&&& \end{array} $$Step 1 : Bring down the leading coefficient to the bottom row.
$$ \begin{array}{c|rrrr}1&\color{orangered}{ 1 }&-3&-9&-5\\& & & & \\ \hline &\color{orangered}{1}&&& \end{array} $$Step 2 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ 1 } \cdot \color{blue}{ 1 } = \color{blue}{ 1 } $.
$$ \begin{array}{c|rrrr}\color{blue}{1}&1&-3&-9&-5\\& & \color{blue}{1} & & \\ \hline &\color{blue}{1}&&& \end{array} $$Step 3 : Add down last column: $ \color{orangered}{ -3 } + \color{orangered}{ 1 } = \color{orangered}{ -2 } $
$$ \begin{array}{c|rrrr}1&1&\color{orangered}{ -3 }&-9&-5\\& & \color{orangered}{1} & & \\ \hline &1&\color{orangered}{-2}&& \end{array} $$Step 4 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ 1 } \cdot \color{blue}{ \left( -2 \right) } = \color{blue}{ -2 } $.
$$ \begin{array}{c|rrrr}\color{blue}{1}&1&-3&-9&-5\\& & 1& \color{blue}{-2} & \\ \hline &1&\color{blue}{-2}&& \end{array} $$Step 5 : Add down last column: $ \color{orangered}{ -9 } + \color{orangered}{ \left( -2 \right) } = \color{orangered}{ -11 } $
$$ \begin{array}{c|rrrr}1&1&-3&\color{orangered}{ -9 }&-5\\& & 1& \color{orangered}{-2} & \\ \hline &1&-2&\color{orangered}{-11}& \end{array} $$Step 6 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ 1 } \cdot \color{blue}{ \left( -11 \right) } = \color{blue}{ -11 } $.
$$ \begin{array}{c|rrrr}\color{blue}{1}&1&-3&-9&-5\\& & 1& -2& \color{blue}{-11} \\ \hline &1&-2&\color{blue}{-11}& \end{array} $$Step 7 : Add down last column: $ \color{orangered}{ -5 } + \color{orangered}{ \left( -11 \right) } = \color{orangered}{ -16 } $
$$ \begin{array}{c|rrrr}1&1&-3&-9&\color{orangered}{ -5 }\\& & 1& -2& \color{orangered}{-11} \\ \hline &\color{blue}{1}&\color{blue}{-2}&\color{blue}{-11}&\color{orangered}{-16} \end{array} $$Bottom line represents the quotient $ \color{blue}{ x^{2}-2x-11 } $ with a remainder of $ \color{red}{ -16 } $.