Divide using synthetic division $$ ( x^{3}+10x^{2}+24x+15 ) \div ( x+3 ) $$
Answer
The synthetic division table is:
$$ \begin{array}{c|rrrr}-3&1&10&24&15\\& & -3& -21& \color{black}{-9} \\ \hline &\color{blue}{1}&\color{blue}{7}&\color{blue}{3}&\color{orangered}{6} \end{array} $$The solution is:
$$ \frac{ x^{3}+10x^{2}+24x+15 }{ x+3 } = \color{blue}{x^{2}+7x+3} ~+~ \frac{ \color{red}{ 6 } }{ x+3 } $$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.
$$ \begin{array}{c|rrrr}\color{blue}{-3}&1&10&24&15\\& & & & \\ \hline &&&& \end{array} $$Step 1 : Bring down the leading coefficient to the bottom row.
$$ \begin{array}{c|rrrr}-3&\color{orangered}{ 1 }&10&24&15\\& & & & \\ \hline &\color{orangered}{1}&&& \end{array} $$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 } $.
$$ \begin{array}{c|rrrr}\color{blue}{-3}&1&10&24&15\\& & \color{blue}{-3} & & \\ \hline &\color{blue}{1}&&& \end{array} $$Step 3 : Add down last column: $ \color{orangered}{ 10 } + \color{orangered}{ \left( -3 \right) } = \color{orangered}{ 7 } $
$$ \begin{array}{c|rrrr}-3&1&\color{orangered}{ 10 }&24&15\\& & \color{orangered}{-3} & & \\ \hline &1&\color{orangered}{7}&& \end{array} $$Step 4 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ -3 } \cdot \color{blue}{ 7 } = \color{blue}{ -21 } $.
$$ \begin{array}{c|rrrr}\color{blue}{-3}&1&10&24&15\\& & -3& \color{blue}{-21} & \\ \hline &1&\color{blue}{7}&& \end{array} $$Step 5 : Add down last column: $ \color{orangered}{ 24 } + \color{orangered}{ \left( -21 \right) } = \color{orangered}{ 3 } $
$$ \begin{array}{c|rrrr}-3&1&10&\color{orangered}{ 24 }&15\\& & -3& \color{orangered}{-21} & \\ \hline &1&7&\color{orangered}{3}& \end{array} $$Step 6 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ -3 } \cdot \color{blue}{ 3 } = \color{blue}{ -9 } $.
$$ \begin{array}{c|rrrr}\color{blue}{-3}&1&10&24&15\\& & -3& -21& \color{blue}{-9} \\ \hline &1&7&\color{blue}{3}& \end{array} $$Step 7 : Add down last column: $ \color{orangered}{ 15 } + \color{orangered}{ \left( -9 \right) } = \color{orangered}{ 6 } $
$$ \begin{array}{c|rrrr}-3&1&10&24&\color{orangered}{ 15 }\\& & -3& -21& \color{orangered}{-9} \\ \hline &\color{blue}{1}&\color{blue}{7}&\color{blue}{3}&\color{orangered}{6} \end{array} $$Bottom line represents the quotient $ \color{blue}{ x^{2}+7x+3 } $ with a remainder of $ \color{red}{ 6 } $.