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:
$$ \color{blue}{ b = -2 } ~ \text{ and } ~ \color{red}{ c = -35 }$$Now we must discover two numbers that sum up to $ \color{blue}{ -2 } $ and multiply to $ \color{red}{ -35 } $.
Step 2: Find out pairs of numbers with a product of $\color{red}{ c = -35 }$.
PRODUCT = -35 | |
-1 35 | 1 -35 |
-5 7 | 5 -7 |
Step 3: Find out which pair sums up to $\color{blue}{ b = -2 }$
PRODUCT = -35 and SUM = -2 | |
-1 35 | 1 -35 |
-5 7 | 5 -7 |
Step 4: Put 5 and -7 into placeholders to get factored form.
$$ \begin{aligned} x^{2}-2x-35 & = (x + \color{orangered}{\square} )(x + \color{orangered}{\square}) \\ x^{2}-2x-35 & = (x + 5)(x -7) \end{aligned} $$