Check if $ x-15 $ is a factor of $ x^{3}-2x^{2}-23x-60 $.
Answer
The synthetic division table is:
$$ \begin{array}{c|rrrr}15&1&-2&-23&-60\\& & 15& 195& \color{black}{2580} \\ \hline &\color{blue}{1}&\color{blue}{13}&\color{blue}{172}&\color{orangered}{2520} \end{array} $$Because the remainder $ \left( \color{red}{ 2520 } \right) $ is not zero, we conclude that the $ x-15 $ is not a factor of $ x^{3}-2x^{2}-23x-60$.
Explanation
First we need to create a synthetic division table.
Step 1 : Write down the coefficients of the dividend into division table. Put the zero from $ x -15 = 0 $ ( $ x = \color{blue}{ 15 } $ ) at the left.
$$ \begin{array}{c|rrrr}\color{blue}{15}&1&-2&-23&-60\\& & & & \\ \hline &&&& \end{array} $$Step 1 : Bring down the leading coefficient to the bottom row.
$$ \begin{array}{c|rrrr}15&\color{orangered}{ 1 }&-2&-23&-60\\& & & & \\ \hline &\color{orangered}{1}&&& \end{array} $$Step 2 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ 15 } \cdot \color{blue}{ 1 } = \color{blue}{ 15 } $.
$$ \begin{array}{c|rrrr}\color{blue}{15}&1&-2&-23&-60\\& & \color{blue}{15} & & \\ \hline &\color{blue}{1}&&& \end{array} $$Step 3 : Add down last column: $ \color{orangered}{ -2 } + \color{orangered}{ 15 } = \color{orangered}{ 13 } $
$$ \begin{array}{c|rrrr}15&1&\color{orangered}{ -2 }&-23&-60\\& & \color{orangered}{15} & & \\ \hline &1&\color{orangered}{13}&& \end{array} $$Step 4 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ 15 } \cdot \color{blue}{ 13 } = \color{blue}{ 195 } $.
$$ \begin{array}{c|rrrr}\color{blue}{15}&1&-2&-23&-60\\& & 15& \color{blue}{195} & \\ \hline &1&\color{blue}{13}&& \end{array} $$Step 5 : Add down last column: $ \color{orangered}{ -23 } + \color{orangered}{ 195 } = \color{orangered}{ 172 } $
$$ \begin{array}{c|rrrr}15&1&-2&\color{orangered}{ -23 }&-60\\& & 15& \color{orangered}{195} & \\ \hline &1&13&\color{orangered}{172}& \end{array} $$Step 6 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ 15 } \cdot \color{blue}{ 172 } = \color{blue}{ 2580 } $.
$$ \begin{array}{c|rrrr}\color{blue}{15}&1&-2&-23&-60\\& & 15& 195& \color{blue}{2580} \\ \hline &1&13&\color{blue}{172}& \end{array} $$Step 7 : Add down last column: $ \color{orangered}{ -60 } + \color{orangered}{ 2580 } = \color{orangered}{ 2520 } $
$$ \begin{array}{c|rrrr}15&1&-2&-23&\color{orangered}{ -60 }\\& & 15& 195& \color{orangered}{2580} \\ \hline &\color{blue}{1}&\color{blue}{13}&\color{blue}{172}&\color{orangered}{2520} \end{array} $$Remainder is the last entry in the bottom row $ \left(\color{red}{ 2520 }\right)$.