Divide using synthetic division $$ ( 5x^{2}+12x+3 ) \div ( x+1 ) $$
Answer
The synthetic division table is:
$$ \begin{array}{c|rrr}-1&5&12&3\\& & -5& \color{black}{-7} \\ \hline &\color{blue}{5}&\color{blue}{7}&\color{orangered}{-4} \end{array} $$The solution is:
$$ \frac{ 5x^{2}+12x+3 }{ x+1 } = \color{blue}{5x+7} \color{red}{~-~} \frac{ \color{red}{ 4 } }{ x+1 } $$Explanation
Step 1 : Write down the coefficients of the dividend into division table. Put the zero from $ x + 1 = 0 $ ( $ x = \color{blue}{ -1 } $ ) at the left.
$$ \begin{array}{c|rrr}\color{blue}{-1}&5&12&3\\& & & \\ \hline &&& \end{array} $$Step 1 : Bring down the leading coefficient to the bottom row.
$$ \begin{array}{c|rrr}-1&\color{orangered}{ 5 }&12&3\\& & & \\ \hline &\color{orangered}{5}&& \end{array} $$Step 2 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ -1 } \cdot \color{blue}{ 5 } = \color{blue}{ -5 } $.
$$ \begin{array}{c|rrr}\color{blue}{-1}&5&12&3\\& & \color{blue}{-5} & \\ \hline &\color{blue}{5}&& \end{array} $$Step 3 : Add down last column: $ \color{orangered}{ 12 } + \color{orangered}{ \left( -5 \right) } = \color{orangered}{ 7 } $
$$ \begin{array}{c|rrr}-1&5&\color{orangered}{ 12 }&3\\& & \color{orangered}{-5} & \\ \hline &5&\color{orangered}{7}& \end{array} $$Step 4 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ -1 } \cdot \color{blue}{ 7 } = \color{blue}{ -7 } $.
$$ \begin{array}{c|rrr}\color{blue}{-1}&5&12&3\\& & -5& \color{blue}{-7} \\ \hline &5&\color{blue}{7}& \end{array} $$Step 5 : Add down last column: $ \color{orangered}{ 3 } + \color{orangered}{ \left( -7 \right) } = \color{orangered}{ -4 } $
$$ \begin{array}{c|rrr}-1&5&12&\color{orangered}{ 3 }\\& & -5& \color{orangered}{-7} \\ \hline &\color{blue}{5}&\color{blue}{7}&\color{orangered}{-4} \end{array} $$Bottom line represents the quotient $ \color{blue}{ 5x+7 } $ with a remainder of $ \color{red}{ -4 } $.