Divide using synthetic division $$ ( -8x^{3}+21x^{2}-20 ) \div ( x-2 ) $$
Answer
The synthetic division table is:
$$ \begin{array}{c|rrrr}2&-8&21&0&-20\\& & -16& 10& \color{black}{20} \\ \hline &\color{blue}{-8}&\color{blue}{5}&\color{blue}{10}&\color{orangered}{0} \end{array} $$The solution is:
$$ \frac{ -8x^{3}+21x^{2}-20 }{ x-2 } = \color{blue}{-8x^{2}+5x+10} $$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.
$$ \begin{array}{c|rrrr}\color{blue}{2}&-8&21&0&-20\\& & & & \\ \hline &&&& \end{array} $$Step 1 : Bring down the leading coefficient to the bottom row.
$$ \begin{array}{c|rrrr}2&\color{orangered}{ -8 }&21&0&-20\\& & & & \\ \hline &\color{orangered}{-8}&&& \end{array} $$Step 2 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ 2 } \cdot \color{blue}{ \left( -8 \right) } = \color{blue}{ -16 } $.
$$ \begin{array}{c|rrrr}\color{blue}{2}&-8&21&0&-20\\& & \color{blue}{-16} & & \\ \hline &\color{blue}{-8}&&& \end{array} $$Step 3 : Add down last column: $ \color{orangered}{ 21 } + \color{orangered}{ \left( -16 \right) } = \color{orangered}{ 5 } $
$$ \begin{array}{c|rrrr}2&-8&\color{orangered}{ 21 }&0&-20\\& & \color{orangered}{-16} & & \\ \hline &-8&\color{orangered}{5}&& \end{array} $$Step 4 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ 2 } \cdot \color{blue}{ 5 } = \color{blue}{ 10 } $.
$$ \begin{array}{c|rrrr}\color{blue}{2}&-8&21&0&-20\\& & -16& \color{blue}{10} & \\ \hline &-8&\color{blue}{5}&& \end{array} $$Step 5 : Add down last column: $ \color{orangered}{ 0 } + \color{orangered}{ 10 } = \color{orangered}{ 10 } $
$$ \begin{array}{c|rrrr}2&-8&21&\color{orangered}{ 0 }&-20\\& & -16& \color{orangered}{10} & \\ \hline &-8&5&\color{orangered}{10}& \end{array} $$Step 6 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ 2 } \cdot \color{blue}{ 10 } = \color{blue}{ 20 } $.
$$ \begin{array}{c|rrrr}\color{blue}{2}&-8&21&0&-20\\& & -16& 10& \color{blue}{20} \\ \hline &-8&5&\color{blue}{10}& \end{array} $$Step 7 : Add down last column: $ \color{orangered}{ -20 } + \color{orangered}{ 20 } = \color{orangered}{ 0 } $
$$ \begin{array}{c|rrrr}2&-8&21&0&\color{orangered}{ -20 }\\& & -16& 10& \color{orangered}{20} \\ \hline &\color{blue}{-8}&\color{blue}{5}&\color{blue}{10}&\color{orangered}{0} \end{array} $$Bottom line represents the quotient $ \color{blue}{ -8x^{2}+5x+10 } $ with a remainder of $ \color{red}{ 0 } $.