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