Divide using synthetic division $$ ( x^{2}+3x-28 ) \div ( x+7 ) $$
Answer
The synthetic division table is:
$$ \begin{array}{c|rrr}-7&1&3&-28\\& & -7& \color{black}{28} \\ \hline &\color{blue}{1}&\color{blue}{-4}&\color{orangered}{0} \end{array} $$The solution is:
$$ \frac{ x^{2}+3x-28 }{ x+7 } = \color{blue}{x-4} $$Explanation
Step 1 : Write down the coefficients of the dividend into division table. Put the zero from $ x + 7 = 0 $ ( $ x = \color{blue}{ -7 } $ ) at the left.
$$ \begin{array}{c|rrr}\color{blue}{-7}&1&3&-28\\& & & \\ \hline &&& \end{array} $$Step 1 : Bring down the leading coefficient to the bottom row.
$$ \begin{array}{c|rrr}-7&\color{orangered}{ 1 }&3&-28\\& & & \\ \hline &\color{orangered}{1}&& \end{array} $$Step 2 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ -7 } \cdot \color{blue}{ 1 } = \color{blue}{ -7 } $.
$$ \begin{array}{c|rrr}\color{blue}{-7}&1&3&-28\\& & \color{blue}{-7} & \\ \hline &\color{blue}{1}&& \end{array} $$Step 3 : Add down last column: $ \color{orangered}{ 3 } + \color{orangered}{ \left( -7 \right) } = \color{orangered}{ -4 } $
$$ \begin{array}{c|rrr}-7&1&\color{orangered}{ 3 }&-28\\& & \color{orangered}{-7} & \\ \hline &1&\color{orangered}{-4}& \end{array} $$Step 4 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ -7 } \cdot \color{blue}{ \left( -4 \right) } = \color{blue}{ 28 } $.
$$ \begin{array}{c|rrr}\color{blue}{-7}&1&3&-28\\& & -7& \color{blue}{28} \\ \hline &1&\color{blue}{-4}& \end{array} $$Step 5 : Add down last column: $ \color{orangered}{ -28 } + \color{orangered}{ 28 } = \color{orangered}{ 0 } $
$$ \begin{array}{c|rrr}-7&1&3&\color{orangered}{ -28 }\\& & -7& \color{orangered}{28} \\ \hline &\color{blue}{1}&\color{blue}{-4}&\color{orangered}{0} \end{array} $$Bottom line represents the quotient $ \color{blue}{ x-4 } $ with a remainder of $ \color{red}{ 0 } $.