Divide using synthetic division $$ ( x^{4}-16x^{2}+5x+20 ) \div ( x+4 ) $$
Answer
The synthetic division table is:
$$ \begin{array}{c|rrrrr}-4&1&0&-16&5&20\\& & -4& 16& 0& \color{black}{-20} \\ \hline &\color{blue}{1}&\color{blue}{-4}&\color{blue}{0}&\color{blue}{5}&\color{orangered}{0} \end{array} $$The solution is:
$$ \frac{ x^{4}-16x^{2}+5x+20 }{ x+4 } = \color{blue}{x^{3}-4x^{2}+5} $$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.
$$ \begin{array}{c|rrrrr}\color{blue}{-4}&1&0&-16&5&20\\& & & & & \\ \hline &&&&& \end{array} $$Step 1 : Bring down the leading coefficient to the bottom row.
$$ \begin{array}{c|rrrrr}-4&\color{orangered}{ 1 }&0&-16&5&20\\& & & & & \\ \hline &\color{orangered}{1}&&&& \end{array} $$Step 2 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ -4 } \cdot \color{blue}{ 1 } = \color{blue}{ -4 } $.
$$ \begin{array}{c|rrrrr}\color{blue}{-4}&1&0&-16&5&20\\& & \color{blue}{-4} & & & \\ \hline &\color{blue}{1}&&&& \end{array} $$Step 3 : Add down last column: $ \color{orangered}{ 0 } + \color{orangered}{ \left( -4 \right) } = \color{orangered}{ -4 } $
$$ \begin{array}{c|rrrrr}-4&1&\color{orangered}{ 0 }&-16&5&20\\& & \color{orangered}{-4} & & & \\ \hline &1&\color{orangered}{-4}&&& \end{array} $$Step 4 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ -4 } \cdot \color{blue}{ \left( -4 \right) } = \color{blue}{ 16 } $.
$$ \begin{array}{c|rrrrr}\color{blue}{-4}&1&0&-16&5&20\\& & -4& \color{blue}{16} & & \\ \hline &1&\color{blue}{-4}&&& \end{array} $$Step 5 : Add down last column: $ \color{orangered}{ -16 } + \color{orangered}{ 16 } = \color{orangered}{ 0 } $
$$ \begin{array}{c|rrrrr}-4&1&0&\color{orangered}{ -16 }&5&20\\& & -4& \color{orangered}{16} & & \\ \hline &1&-4&\color{orangered}{0}&& \end{array} $$Step 6 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ -4 } \cdot \color{blue}{ 0 } = \color{blue}{ 0 } $.
$$ \begin{array}{c|rrrrr}\color{blue}{-4}&1&0&-16&5&20\\& & -4& 16& \color{blue}{0} & \\ \hline &1&-4&\color{blue}{0}&& \end{array} $$Step 7 : Add down last column: $ \color{orangered}{ 5 } + \color{orangered}{ 0 } = \color{orangered}{ 5 } $
$$ \begin{array}{c|rrrrr}-4&1&0&-16&\color{orangered}{ 5 }&20\\& & -4& 16& \color{orangered}{0} & \\ \hline &1&-4&0&\color{orangered}{5}& \end{array} $$Step 8 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ -4 } \cdot \color{blue}{ 5 } = \color{blue}{ -20 } $.
$$ \begin{array}{c|rrrrr}\color{blue}{-4}&1&0&-16&5&20\\& & -4& 16& 0& \color{blue}{-20} \\ \hline &1&-4&0&\color{blue}{5}& \end{array} $$Step 9 : Add down last column: $ \color{orangered}{ 20 } + \color{orangered}{ \left( -20 \right) } = \color{orangered}{ 0 } $
$$ \begin{array}{c|rrrrr}-4&1&0&-16&5&\color{orangered}{ 20 }\\& & -4& 16& 0& \color{orangered}{-20} \\ \hline &\color{blue}{1}&\color{blue}{-4}&\color{blue}{0}&\color{blue}{5}&\color{orangered}{0} \end{array} $$Bottom line represents the quotient $ \color{blue}{ x^{3}-4x^{2}+5 } $ with a remainder of $ \color{red}{ 0 } $.