Step 1: Identify constants $ \color{blue}{ b }$ and $\color{red}{ c }$. ( $ \color{blue}{ b }$ is a number in front of the $ x $ term and $ \color{red}{ c } $ is a constant). In our case:
$$ \color{blue}{ b = -3 } ~ \text{ and } ~ \color{red}{ c = -10 }$$Now we must discover two numbers that sum up to $ \color{blue}{ -3 } $ and multiply to $ \color{red}{ -10 } $.
Step 2: Find out pairs of numbers with a product of $\color{red}{ c = -10 }$.
PRODUCT = -10 | |
-1 10 | 1 -10 |
-2 5 | 2 -5 |
Step 3: Find out which pair sums up to $\color{blue}{ b = -3 }$
PRODUCT = -10 and SUM = -3 | |
-1 10 | 1 -10 |
-2 5 | 2 -5 |
Step 4: Put 2 and -5 into placeholders to get factored form.
$$ \begin{aligned} x^{2}-3x-10 & = (x + \color{orangered}{\square} )(x + \color{orangered}{\square}) \\ x^{2}-3x-10 & = (x + 2)(x -5) \end{aligned} $$