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:
$$ \color{blue}{ b = -18 } ~ \text{ and } ~ \color{red}{ c = -19 }$$Now we must discover two numbers that sum up to $ \color{blue}{ -18 } $ and multiply to $ \color{red}{ -19 } $.
Step 2: Find out pairs of numbers with a product of $\color{red}{ c = -19 }$.
PRODUCT = -19 | |
-1 19 | 1 -19 |
Step 3: Find out which pair sums up to $\color{blue}{ b = -18 }$
PRODUCT = -19 and SUM = -18 | |
-1 19 | 1 -19 |
Step 4: Put 1 and -19 into placeholders to get factored form.
$$ \begin{aligned} t^{2}-18t-19 & = (x + \color{orangered}{\square} )(x + \color{orangered}{\square}) \\ t^{2}-18t-19 & = (x + 1)(x -19) \end{aligned} $$