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:
$$ \color{blue}{ b = -6 } ~ \text{ and } ~ \color{red}{ c = -55 }$$Now we must discover two numbers that sum up to $ \color{blue}{ -6 } $ and multiply to $ \color{red}{ -55 } $.
Step 2: Find out pairs of numbers with a product of $\color{red}{ c = -55 }$.
PRODUCT = -55 | |
-1 55 | 1 -55 |
-5 11 | 5 -11 |
Step 3: Find out which pair sums up to $\color{blue}{ b = -6 }$
PRODUCT = -55 and SUM = -6 | |
-1 55 | 1 -55 |
-5 11 | 5 -11 |
Step 4: Put 5 and -11 into placeholders to get factored form.
$$ \begin{aligned} x^{2}-6x-55 & = (x + \color{orangered}{\square} )(x + \color{orangered}{\square}) \\ x^{2}-6x-55 & = (x + 5)(x -11) \end{aligned} $$