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:
$$ \color{blue}{ b = -6 } ~ \text{ and } ~ \color{red}{ c = -27 }$$Now we must discover two numbers that sum up to $ \color{blue}{ -6 } $ and multiply to $ \color{red}{ -27 } $.
Step 2: Find out pairs of numbers with a product of $\color{red}{ c = -27 }$.
PRODUCT = -27 | |
-1 27 | 1 -27 |
-3 9 | 3 -9 |
Step 3: Find out which pair sums up to $\color{blue}{ b = -6 }$
PRODUCT = -27 and SUM = -6 | |
-1 27 | 1 -27 |
-3 9 | 3 -9 |
Step 4: Put 3 and -9 into placeholders to get factored form.
$$ \begin{aligned} g^{2}-6g-27 & = (x + \color{orangered}{\square} )(x + \color{orangered}{\square}) \\ g^{2}-6g-27 & = (x + 3)(x -9) \end{aligned} $$