Divide using synthetic division $$ ( 5x^{2}+12 ) \div ( x-3 ) $$
Answer
The synthetic division table is:
$$ \begin{array}{c|rrr}3&5&0&12\\& & 15& \color{black}{45} \\ \hline &\color{blue}{5}&\color{blue}{15}&\color{orangered}{57} \end{array} $$The solution is:
$$ \frac{ 5x^{2}+12 }{ x-3 } = \color{blue}{5x+15} ~+~ \frac{ \color{red}{ 57 } }{ x-3 } $$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.
$$ \begin{array}{c|rrr}\color{blue}{3}&5&0&12\\& & & \\ \hline &&& \end{array} $$Step 1 : Bring down the leading coefficient to the bottom row.
$$ \begin{array}{c|rrr}3&\color{orangered}{ 5 }&0&12\\& & & \\ \hline &\color{orangered}{5}&& \end{array} $$Step 2 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ 3 } \cdot \color{blue}{ 5 } = \color{blue}{ 15 } $.
$$ \begin{array}{c|rrr}\color{blue}{3}&5&0&12\\& & \color{blue}{15} & \\ \hline &\color{blue}{5}&& \end{array} $$Step 3 : Add down last column: $ \color{orangered}{ 0 } + \color{orangered}{ 15 } = \color{orangered}{ 15 } $
$$ \begin{array}{c|rrr}3&5&\color{orangered}{ 0 }&12\\& & \color{orangered}{15} & \\ \hline &5&\color{orangered}{15}& \end{array} $$Step 4 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ 3 } \cdot \color{blue}{ 15 } = \color{blue}{ 45 } $.
$$ \begin{array}{c|rrr}\color{blue}{3}&5&0&12\\& & 15& \color{blue}{45} \\ \hline &5&\color{blue}{15}& \end{array} $$Step 5 : Add down last column: $ \color{orangered}{ 12 } + \color{orangered}{ 45 } = \color{orangered}{ 57 } $
$$ \begin{array}{c|rrr}3&5&0&\color{orangered}{ 12 }\\& & 15& \color{orangered}{45} \\ \hline &\color{blue}{5}&\color{blue}{15}&\color{orangered}{57} \end{array} $$Bottom line represents the quotient $ \color{blue}{ 5x+15 } $ with a remainder of $ \color{red}{ 57 } $.