Check if $ x+2 $ is a factor of $ x^{2}-3x-10 $.
Answer
The synthetic division table is:
$$ \begin{array}{c|rrr}-2&1&-3&-10\\& & -2& \color{black}{10} \\ \hline &\color{blue}{1}&\color{blue}{-5}&\color{orangered}{0} \end{array} $$Because the remainder equals zero, we conclude that the $ x+2 $ is a factor of the $ x^{2}-3x-10 $.
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 + 2 = 0 $ ( $ x = \color{blue}{ -2 } $ ) at the left.
$$ \begin{array}{c|rrr}\color{blue}{-2}&1&-3&-10\\& & & \\ \hline &&& \end{array} $$Step 1 : Bring down the leading coefficient to the bottom row.
$$ \begin{array}{c|rrr}-2&\color{orangered}{ 1 }&-3&-10\\& & & \\ \hline &\color{orangered}{1}&& \end{array} $$Step 2 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ -2 } \cdot \color{blue}{ 1 } = \color{blue}{ -2 } $.
$$ \begin{array}{c|rrr}\color{blue}{-2}&1&-3&-10\\& & \color{blue}{-2} & \\ \hline &\color{blue}{1}&& \end{array} $$Step 3 : Add down last column: $ \color{orangered}{ -3 } + \color{orangered}{ \left( -2 \right) } = \color{orangered}{ -5 } $
$$ \begin{array}{c|rrr}-2&1&\color{orangered}{ -3 }&-10\\& & \color{orangered}{-2} & \\ \hline &1&\color{orangered}{-5}& \end{array} $$Step 4 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ -2 } \cdot \color{blue}{ \left( -5 \right) } = \color{blue}{ 10 } $.
$$ \begin{array}{c|rrr}\color{blue}{-2}&1&-3&-10\\& & -2& \color{blue}{10} \\ \hline &1&\color{blue}{-5}& \end{array} $$Step 5 : Add down last column: $ \color{orangered}{ -10 } + \color{orangered}{ 10 } = \color{orangered}{ 0 } $
$$ \begin{array}{c|rrr}-2&1&-3&\color{orangered}{ -10 }\\& & -2& \color{orangered}{10} \\ \hline &\color{blue}{1}&\color{blue}{-5}&\color{orangered}{0} \end{array} $$Remainder is the last entry in the bottom row $ \left(\color{red}{ 0 }\right)$.