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