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