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:
$$ \color{blue}{ b = -7 } ~ \text{ and } ~ \color{red}{ c = -30 }$$Now we must discover two numbers that sum up to $ \color{blue}{ -7 } $ and multiply to $ \color{red}{ -30 } $.
Step 2: Find out pairs of numbers with a product of $\color{red}{ c = -30 }$.
PRODUCT = -30 | |
-1 30 | 1 -30 |
-2 15 | 2 -15 |
-3 10 | 3 -10 |
-5 6 | 5 -6 |
Step 3: Find out which pair sums up to $\color{blue}{ b = -7 }$
PRODUCT = -30 and SUM = -7 | |
-1 30 | 1 -30 |
-2 15 | 2 -15 |
-3 10 | 3 -10 |
-5 6 | 5 -6 |
Step 4: Put 3 and -10 into placeholders to get factored form.
$$ \begin{aligned} x^{2}-7x-30 & = (x + \color{orangered}{\square} )(x + \color{orangered}{\square}) \\ x^{2}-7x-30 & = (x + 3)(x -10) \end{aligned} $$