Find remainder when $ 3x^{3}-7x^{2}+6x-14 $ is divided by $ x+7 $.
Answer
The synthetic division table is:
$$ \begin{array}{c|rrrr}-7&3&-7&6&-14\\& & -21& 196& \color{black}{-1414} \\ \hline &\color{blue}{3}&\color{blue}{-28}&\color{blue}{202}&\color{orangered}{-1428} \end{array} $$The remainder when $ 3x^{3}-7x^{2}+6x-14 $ is divided by $ x+7 $ is $ \, \color{red}{ -1428 } $.
Explanation
We can find remainder using synthetic division method.
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.
$$ \begin{array}{c|rrrr}\color{blue}{-7}&3&-7&6&-14\\& & & & \\ \hline &&&& \end{array} $$Step 1 : Bring down the leading coefficient to the bottom row.
$$ \begin{array}{c|rrrr}-7&\color{orangered}{ 3 }&-7&6&-14\\& & & & \\ \hline &\color{orangered}{3}&&& \end{array} $$Step 2 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ -7 } \cdot \color{blue}{ 3 } = \color{blue}{ -21 } $.
$$ \begin{array}{c|rrrr}\color{blue}{-7}&3&-7&6&-14\\& & \color{blue}{-21} & & \\ \hline &\color{blue}{3}&&& \end{array} $$Step 3 : Add down last column: $ \color{orangered}{ -7 } + \color{orangered}{ \left( -21 \right) } = \color{orangered}{ -28 } $
$$ \begin{array}{c|rrrr}-7&3&\color{orangered}{ -7 }&6&-14\\& & \color{orangered}{-21} & & \\ \hline &3&\color{orangered}{-28}&& \end{array} $$Step 4 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ -7 } \cdot \color{blue}{ \left( -28 \right) } = \color{blue}{ 196 } $.
$$ \begin{array}{c|rrrr}\color{blue}{-7}&3&-7&6&-14\\& & -21& \color{blue}{196} & \\ \hline &3&\color{blue}{-28}&& \end{array} $$Step 5 : Add down last column: $ \color{orangered}{ 6 } + \color{orangered}{ 196 } = \color{orangered}{ 202 } $
$$ \begin{array}{c|rrrr}-7&3&-7&\color{orangered}{ 6 }&-14\\& & -21& \color{orangered}{196} & \\ \hline &3&-28&\color{orangered}{202}& \end{array} $$Step 6 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ -7 } \cdot \color{blue}{ 202 } = \color{blue}{ -1414 } $.
$$ \begin{array}{c|rrrr}\color{blue}{-7}&3&-7&6&-14\\& & -21& 196& \color{blue}{-1414} \\ \hline &3&-28&\color{blue}{202}& \end{array} $$Step 7 : Add down last column: $ \color{orangered}{ -14 } + \color{orangered}{ \left( -1414 \right) } = \color{orangered}{ -1428 } $
$$ \begin{array}{c|rrrr}-7&3&-7&6&\color{orangered}{ -14 }\\& & -21& 196& \color{orangered}{-1414} \\ \hline &\color{blue}{3}&\color{blue}{-28}&\color{blue}{202}&\color{orangered}{-1428} \end{array} $$Remainder is the last entry in the bottom row $ \left(\color{red}{ -1428 }\right) $.