Find remainder when $ 3x^{3}-30x+24 $ is divided by $ x-2 $.
Answer
The synthetic division table is:
$$ \begin{array}{c|rrrr}2&3&0&-30&24\\& & 6& 12& \color{black}{-36} \\ \hline &\color{blue}{3}&\color{blue}{6}&\color{blue}{-18}&\color{orangered}{-12} \end{array} $$The remainder when $ 3x^{3}-30x+24 $ is divided by $ x-2 $ is $ \, \color{red}{ -12 } $.
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 -2 = 0 $ ( $ x = \color{blue}{ 2 } $ ) at the left.
$$ \begin{array}{c|rrrr}\color{blue}{2}&3&0&-30&24\\& & & & \\ \hline &&&& \end{array} $$Step 1 : Bring down the leading coefficient to the bottom row.
$$ \begin{array}{c|rrrr}2&\color{orangered}{ 3 }&0&-30&24\\& & & & \\ \hline &\color{orangered}{3}&&& \end{array} $$Step 2 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ 2 } \cdot \color{blue}{ 3 } = \color{blue}{ 6 } $.
$$ \begin{array}{c|rrrr}\color{blue}{2}&3&0&-30&24\\& & \color{blue}{6} & & \\ \hline &\color{blue}{3}&&& \end{array} $$Step 3 : Add down last column: $ \color{orangered}{ 0 } + \color{orangered}{ 6 } = \color{orangered}{ 6 } $
$$ \begin{array}{c|rrrr}2&3&\color{orangered}{ 0 }&-30&24\\& & \color{orangered}{6} & & \\ \hline &3&\color{orangered}{6}&& \end{array} $$Step 4 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ 2 } \cdot \color{blue}{ 6 } = \color{blue}{ 12 } $.
$$ \begin{array}{c|rrrr}\color{blue}{2}&3&0&-30&24\\& & 6& \color{blue}{12} & \\ \hline &3&\color{blue}{6}&& \end{array} $$Step 5 : Add down last column: $ \color{orangered}{ -30 } + \color{orangered}{ 12 } = \color{orangered}{ -18 } $
$$ \begin{array}{c|rrrr}2&3&0&\color{orangered}{ -30 }&24\\& & 6& \color{orangered}{12} & \\ \hline &3&6&\color{orangered}{-18}& \end{array} $$Step 6 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ 2 } \cdot \color{blue}{ \left( -18 \right) } = \color{blue}{ -36 } $.
$$ \begin{array}{c|rrrr}\color{blue}{2}&3&0&-30&24\\& & 6& 12& \color{blue}{-36} \\ \hline &3&6&\color{blue}{-18}& \end{array} $$Step 7 : Add down last column: $ \color{orangered}{ 24 } + \color{orangered}{ \left( -36 \right) } = \color{orangered}{ -12 } $
$$ \begin{array}{c|rrrr}2&3&0&-30&\color{orangered}{ 24 }\\& & 6& 12& \color{orangered}{-36} \\ \hline &\color{blue}{3}&\color{blue}{6}&\color{blue}{-18}&\color{orangered}{-12} \end{array} $$Remainder is the last entry in the bottom row $ \left(\color{red}{ -12 }\right) $.