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:
$$ \color{blue}{ b = 13 } ~ \text{ and } ~ \color{red}{ c = 42 }$$Now we must discover two numbers that sum up to $ \color{blue}{ 13 } $ and multiply to $ \color{red}{ 42 } $.
Step 2: Find out pairs of numbers with a product of $\color{red}{ c = 42 }$.
PRODUCT = 42 | |
1 42 | -1 -42 |
2 21 | -2 -21 |
3 14 | -3 -14 |
6 7 | -6 -7 |
Step 3: Find out which pair sums up to $\color{blue}{ b = 13 }$
PRODUCT = 42 and SUM = 13 | |
1 42 | -1 -42 |
2 21 | -2 -21 |
3 14 | -3 -14 |
6 7 | -6 -7 |
Step 4: Put 6 and 7 into placeholders to get factored form.
$$ \begin{aligned} x^{2}+13x+42 & = (x + \color{orangered}{\square} )(x + \color{orangered}{\square}) \\ x^{2}+13x+42 & = (x + 6)(x + 7) \end{aligned} $$