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:
$$ \color{blue}{ b = -11 } ~ \text{ and } ~ \color{red}{ c = 18 }$$Now we must discover two numbers that sum up to $ \color{blue}{ -11 } $ and multiply to $ \color{red}{ 18 } $.
Step 2: Find out pairs of numbers with a product of $\color{red}{ c = 18 }$.
PRODUCT = 18 | |
1 18 | -1 -18 |
2 9 | -2 -9 |
3 6 | -3 -6 |
Step 3: Find out which pair sums up to $\color{blue}{ b = -11 }$
PRODUCT = 18 and SUM = -11 | |
1 18 | -1 -18 |
2 9 | -2 -9 |
3 6 | -3 -6 |
Step 4: Put -2 and -9 into placeholders to get factored form.
$$ \begin{aligned} m^{2}-11m+18 & = (x + \color{orangered}{\square} )(x + \color{orangered}{\square}) \\ m^{2}-11m+18 & = (x -2)(x -9) \end{aligned} $$