Find remainder when $ 3x^{3}+2x^{2}-x $ is divided by $ x-2 $.
Answer
The synthetic division table is:
$$ \begin{array}{c|rrrr}2&3&2&-1&0\\& & 6& 16& \color{black}{30} \\ \hline &\color{blue}{3}&\color{blue}{8}&\color{blue}{15}&\color{orangered}{30} \end{array} $$The remainder when $ 3x^{3}+2x^{2}-x $ is divided by $ x-2 $ is $ \, \color{red}{ 30 } $.
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.
$$ \begin{array}{c|rrrr}\color{blue}{2}&3&2&-1&0\\& & & & \\ \hline &&&& \end{array} $$Step 1 : Bring down the leading coefficient to the bottom row.
$$ \begin{array}{c|rrrr}2&\color{orangered}{ 3 }&2&-1&0\\& & & & \\ \hline &\color{orangered}{3}&&& \end{array} $$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 } $.
$$ \begin{array}{c|rrrr}\color{blue}{2}&3&2&-1&0\\& & \color{blue}{6} & & \\ \hline &\color{blue}{3}&&& \end{array} $$Step 3 : Add down last column: $ \color{orangered}{ 2 } + \color{orangered}{ 6 } = \color{orangered}{ 8 } $
$$ \begin{array}{c|rrrr}2&3&\color{orangered}{ 2 }&-1&0\\& & \color{orangered}{6} & & \\ \hline &3&\color{orangered}{8}&& \end{array} $$Step 4 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ 2 } \cdot \color{blue}{ 8 } = \color{blue}{ 16 } $.
$$ \begin{array}{c|rrrr}\color{blue}{2}&3&2&-1&0\\& & 6& \color{blue}{16} & \\ \hline &3&\color{blue}{8}&& \end{array} $$Step 5 : Add down last column: $ \color{orangered}{ -1 } + \color{orangered}{ 16 } = \color{orangered}{ 15 } $
$$ \begin{array}{c|rrrr}2&3&2&\color{orangered}{ -1 }&0\\& & 6& \color{orangered}{16} & \\ \hline &3&8&\color{orangered}{15}& \end{array} $$Step 6 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ 2 } \cdot \color{blue}{ 15 } = \color{blue}{ 30 } $.
$$ \begin{array}{c|rrrr}\color{blue}{2}&3&2&-1&0\\& & 6& 16& \color{blue}{30} \\ \hline &3&8&\color{blue}{15}& \end{array} $$Step 7 : Add down last column: $ \color{orangered}{ 0 } + \color{orangered}{ 30 } = \color{orangered}{ 30 } $
$$ \begin{array}{c|rrrr}2&3&2&-1&\color{orangered}{ 0 }\\& & 6& 16& \color{orangered}{30} \\ \hline &\color{blue}{3}&\color{blue}{8}&\color{blue}{15}&\color{orangered}{30} \end{array} $$Remainder is the last entry in the bottom row $ \left(\color{red}{ 30 }\right) $.