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:
$$ \color{blue}{ b = -12 } ~ \text{ and } ~ \color{red}{ c = 27 }$$Now we must discover two numbers that sum up to $ \color{blue}{ -12 } $ 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 $\color{blue}{ b = -12 }$
PRODUCT = 27 and SUM = -12 | |
1 27 | -1 -27 |
3 9 | -3 -9 |
Step 4: Put -3 and -9 into placeholders to get factored form.
$$ \begin{aligned} x^{2}-12x+27 & = (x + \color{orangered}{\square} )(x + \color{orangered}{\square}) \\ x^{2}-12x+27 & = (x -3)(x -9) \end{aligned} $$