Check if $ x+5 $ is a factor of $ x^{3}+2x^{2}-23x-60 $.
Answer
The synthetic division table is:
$$ \begin{array}{c|rrrr}-5&1&2&-23&-60\\& & -5& 15& \color{black}{40} \\ \hline &\color{blue}{1}&\color{blue}{-3}&\color{blue}{-8}&\color{orangered}{-20} \end{array} $$Because the remainder $ \left( \color{red}{ -20 } \right) $ is not zero, we conclude that the $ x+5 $ 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 + 5 = 0 $ ( $ x = \color{blue}{ -5 } $ ) at the left.
$$ \begin{array}{c|rrrr}\color{blue}{-5}&1&2&-23&-60\\& & & & \\ \hline &&&& \end{array} $$Step 1 : Bring down the leading coefficient to the bottom row.
$$ \begin{array}{c|rrrr}-5&\color{orangered}{ 1 }&2&-23&-60\\& & & & \\ \hline &\color{orangered}{1}&&& \end{array} $$Step 2 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ -5 } \cdot \color{blue}{ 1 } = \color{blue}{ -5 } $.
$$ \begin{array}{c|rrrr}\color{blue}{-5}&1&2&-23&-60\\& & \color{blue}{-5} & & \\ \hline &\color{blue}{1}&&& \end{array} $$Step 3 : Add down last column: $ \color{orangered}{ 2 } + \color{orangered}{ \left( -5 \right) } = \color{orangered}{ -3 } $
$$ \begin{array}{c|rrrr}-5&1&\color{orangered}{ 2 }&-23&-60\\& & \color{orangered}{-5} & & \\ \hline &1&\color{orangered}{-3}&& \end{array} $$Step 4 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ -5 } \cdot \color{blue}{ \left( -3 \right) } = \color{blue}{ 15 } $.
$$ \begin{array}{c|rrrr}\color{blue}{-5}&1&2&-23&-60\\& & -5& \color{blue}{15} & \\ \hline &1&\color{blue}{-3}&& \end{array} $$Step 5 : Add down last column: $ \color{orangered}{ -23 } + \color{orangered}{ 15 } = \color{orangered}{ -8 } $
$$ \begin{array}{c|rrrr}-5&1&2&\color{orangered}{ -23 }&-60\\& & -5& \color{orangered}{15} & \\ \hline &1&-3&\color{orangered}{-8}& \end{array} $$Step 6 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ -5 } \cdot \color{blue}{ \left( -8 \right) } = \color{blue}{ 40 } $.
$$ \begin{array}{c|rrrr}\color{blue}{-5}&1&2&-23&-60\\& & -5& 15& \color{blue}{40} \\ \hline &1&-3&\color{blue}{-8}& \end{array} $$Step 7 : Add down last column: $ \color{orangered}{ -60 } + \color{orangered}{ 40 } = \color{orangered}{ -20 } $
$$ \begin{array}{c|rrrr}-5&1&2&-23&\color{orangered}{ -60 }\\& & -5& 15& \color{orangered}{40} \\ \hline &\color{blue}{1}&\color{blue}{-3}&\color{blue}{-8}&\color{orangered}{-20} \end{array} $$Remainder is the last entry in the bottom row $ \left(\color{red}{ -20 }\right)$.