Divide using synthetic division $$ ( x^{3}-x^{2}+21x-45 ) \div ( x-3 ) $$
Answer
The synthetic division table is:
$$ \begin{array}{c|rrrr}3&1&-1&21&-45\\& & 3& 6& \color{black}{81} \\ \hline &\color{blue}{1}&\color{blue}{2}&\color{blue}{27}&\color{orangered}{36} \end{array} $$The solution is:
$$ \frac{ x^{3}-x^{2}+21x-45 }{ x-3 } = \color{blue}{x^{2}+2x+27} ~+~ \frac{ \color{red}{ 36 } }{ x-3 } $$Explanation
Step 1 : Write down the coefficients of the dividend into division table. Put the zero from $ x -3 = 0 $ ( $ x = \color{blue}{ 3 } $ ) at the left.
$$ \begin{array}{c|rrrr}\color{blue}{3}&1&-1&21&-45\\& & & & \\ \hline &&&& \end{array} $$Step 1 : Bring down the leading coefficient to the bottom row.
$$ \begin{array}{c|rrrr}3&\color{orangered}{ 1 }&-1&21&-45\\& & & & \\ \hline &\color{orangered}{1}&&& \end{array} $$Step 2 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ 3 } \cdot \color{blue}{ 1 } = \color{blue}{ 3 } $.
$$ \begin{array}{c|rrrr}\color{blue}{3}&1&-1&21&-45\\& & \color{blue}{3} & & \\ \hline &\color{blue}{1}&&& \end{array} $$Step 3 : Add down last column: $ \color{orangered}{ -1 } + \color{orangered}{ 3 } = \color{orangered}{ 2 } $
$$ \begin{array}{c|rrrr}3&1&\color{orangered}{ -1 }&21&-45\\& & \color{orangered}{3} & & \\ \hline &1&\color{orangered}{2}&& \end{array} $$Step 4 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ 3 } \cdot \color{blue}{ 2 } = \color{blue}{ 6 } $.
$$ \begin{array}{c|rrrr}\color{blue}{3}&1&-1&21&-45\\& & 3& \color{blue}{6} & \\ \hline &1&\color{blue}{2}&& \end{array} $$Step 5 : Add down last column: $ \color{orangered}{ 21 } + \color{orangered}{ 6 } = \color{orangered}{ 27 } $
$$ \begin{array}{c|rrrr}3&1&-1&\color{orangered}{ 21 }&-45\\& & 3& \color{orangered}{6} & \\ \hline &1&2&\color{orangered}{27}& \end{array} $$Step 6 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ 3 } \cdot \color{blue}{ 27 } = \color{blue}{ 81 } $.
$$ \begin{array}{c|rrrr}\color{blue}{3}&1&-1&21&-45\\& & 3& 6& \color{blue}{81} \\ \hline &1&2&\color{blue}{27}& \end{array} $$Step 7 : Add down last column: $ \color{orangered}{ -45 } + \color{orangered}{ 81 } = \color{orangered}{ 36 } $
$$ \begin{array}{c|rrrr}3&1&-1&21&\color{orangered}{ -45 }\\& & 3& 6& \color{orangered}{81} \\ \hline &\color{blue}{1}&\color{blue}{2}&\color{blue}{27}&\color{orangered}{36} \end{array} $$Bottom line represents the quotient $ \color{blue}{ x^{2}+2x+27 } $ with a remainder of $ \color{red}{ 36 } $.