Divide using synthetic division $$ ( 5x^{3}-16x+64 ) \div ( x+2 ) $$
Answer
The synthetic division table is:
$$ \begin{array}{c|rrrr}-2&5&0&-16&64\\& & -10& 20& \color{black}{-8} \\ \hline &\color{blue}{5}&\color{blue}{-10}&\color{blue}{4}&\color{orangered}{56} \end{array} $$The solution is:
$$ \frac{ 5x^{3}-16x+64 }{ x+2 } = \color{blue}{5x^{2}-10x+4} ~+~ \frac{ \color{red}{ 56 } }{ x+2 } $$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.
$$ \begin{array}{c|rrrr}\color{blue}{-2}&5&0&-16&64\\& & & & \\ \hline &&&& \end{array} $$Step 1 : Bring down the leading coefficient to the bottom row.
$$ \begin{array}{c|rrrr}-2&\color{orangered}{ 5 }&0&-16&64\\& & & & \\ \hline &\color{orangered}{5}&&& \end{array} $$Step 2 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ -2 } \cdot \color{blue}{ 5 } = \color{blue}{ -10 } $.
$$ \begin{array}{c|rrrr}\color{blue}{-2}&5&0&-16&64\\& & \color{blue}{-10} & & \\ \hline &\color{blue}{5}&&& \end{array} $$Step 3 : Add down last column: $ \color{orangered}{ 0 } + \color{orangered}{ \left( -10 \right) } = \color{orangered}{ -10 } $
$$ \begin{array}{c|rrrr}-2&5&\color{orangered}{ 0 }&-16&64\\& & \color{orangered}{-10} & & \\ \hline &5&\color{orangered}{-10}&& \end{array} $$Step 4 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ -2 } \cdot \color{blue}{ \left( -10 \right) } = \color{blue}{ 20 } $.
$$ \begin{array}{c|rrrr}\color{blue}{-2}&5&0&-16&64\\& & -10& \color{blue}{20} & \\ \hline &5&\color{blue}{-10}&& \end{array} $$Step 5 : Add down last column: $ \color{orangered}{ -16 } + \color{orangered}{ 20 } = \color{orangered}{ 4 } $
$$ \begin{array}{c|rrrr}-2&5&0&\color{orangered}{ -16 }&64\\& & -10& \color{orangered}{20} & \\ \hline &5&-10&\color{orangered}{4}& \end{array} $$Step 6 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ -2 } \cdot \color{blue}{ 4 } = \color{blue}{ -8 } $.
$$ \begin{array}{c|rrrr}\color{blue}{-2}&5&0&-16&64\\& & -10& 20& \color{blue}{-8} \\ \hline &5&-10&\color{blue}{4}& \end{array} $$Step 7 : Add down last column: $ \color{orangered}{ 64 } + \color{orangered}{ \left( -8 \right) } = \color{orangered}{ 56 } $
$$ \begin{array}{c|rrrr}-2&5&0&-16&\color{orangered}{ 64 }\\& & -10& 20& \color{orangered}{-8} \\ \hline &\color{blue}{5}&\color{blue}{-10}&\color{blue}{4}&\color{orangered}{56} \end{array} $$Bottom line represents the quotient $ \color{blue}{ 5x^{2}-10x+4 } $ with a remainder of $ \color{red}{ 56 } $.