Divide using synthetic division $$ ( x^{3}-9x^{2}+12x-8 ) \div ( x+2 ) $$
Answer
The synthetic division table is:
$$ \begin{array}{c|rrrr}-2&1&-9&12&-8\\& & -2& 22& \color{black}{-68} \\ \hline &\color{blue}{1}&\color{blue}{-11}&\color{blue}{34}&\color{orangered}{-76} \end{array} $$The solution is:
$$ \frac{ x^{3}-9x^{2}+12x-8 }{ x+2 } = \color{blue}{x^{2}-11x+34} \color{red}{~-~} \frac{ \color{red}{ 76 } }{ x+2 } $$Explanation
Step 1 : Write down the coefficients of the dividend into division table. Put the zero from $ x + 2 = 0 $ ( $ x = \color{blue}{ -2 } $ ) at the left.
$$ \begin{array}{c|rrrr}\color{blue}{-2}&1&-9&12&-8\\& & & & \\ \hline &&&& \end{array} $$Step 1 : Bring down the leading coefficient to the bottom row.
$$ \begin{array}{c|rrrr}-2&\color{orangered}{ 1 }&-9&12&-8\\& & & & \\ \hline &\color{orangered}{1}&&& \end{array} $$Step 2 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ -2 } \cdot \color{blue}{ 1 } = \color{blue}{ -2 } $.
$$ \begin{array}{c|rrrr}\color{blue}{-2}&1&-9&12&-8\\& & \color{blue}{-2} & & \\ \hline &\color{blue}{1}&&& \end{array} $$Step 3 : Add down last column: $ \color{orangered}{ -9 } + \color{orangered}{ \left( -2 \right) } = \color{orangered}{ -11 } $
$$ \begin{array}{c|rrrr}-2&1&\color{orangered}{ -9 }&12&-8\\& & \color{orangered}{-2} & & \\ \hline &1&\color{orangered}{-11}&& \end{array} $$Step 4 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ -2 } \cdot \color{blue}{ \left( -11 \right) } = \color{blue}{ 22 } $.
$$ \begin{array}{c|rrrr}\color{blue}{-2}&1&-9&12&-8\\& & -2& \color{blue}{22} & \\ \hline &1&\color{blue}{-11}&& \end{array} $$Step 5 : Add down last column: $ \color{orangered}{ 12 } + \color{orangered}{ 22 } = \color{orangered}{ 34 } $
$$ \begin{array}{c|rrrr}-2&1&-9&\color{orangered}{ 12 }&-8\\& & -2& \color{orangered}{22} & \\ \hline &1&-11&\color{orangered}{34}& \end{array} $$Step 6 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ -2 } \cdot \color{blue}{ 34 } = \color{blue}{ -68 } $.
$$ \begin{array}{c|rrrr}\color{blue}{-2}&1&-9&12&-8\\& & -2& 22& \color{blue}{-68} \\ \hline &1&-11&\color{blue}{34}& \end{array} $$Step 7 : Add down last column: $ \color{orangered}{ -8 } + \color{orangered}{ \left( -68 \right) } = \color{orangered}{ -76 } $
$$ \begin{array}{c|rrrr}-2&1&-9&12&\color{orangered}{ -8 }\\& & -2& 22& \color{orangered}{-68} \\ \hline &\color{blue}{1}&\color{blue}{-11}&\color{blue}{34}&\color{orangered}{-76} \end{array} $$Bottom line represents the quotient $ \color{blue}{ x^{2}-11x+34 } $ with a remainder of $ \color{red}{ -76 } $.