Step 1 :
After factoring out $ 3 $ we have:
$$ 3x^{2}-57x+180 = 3 ( x^{2}-19x+60 ) $$Step 2 :
Step 2: 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:
$$ \color{blue}{ b = -19 } ~ \text{ and } ~ \color{red}{ c = 60 }$$Now we must discover two numbers that sum up to $ \color{blue}{ -19 } $ and multiply to $ \color{red}{ 60 } $.
Step 3: Find out pairs of numbers with a product of $\color{red}{ c = 60 }$.
PRODUCT = 60 | |
1 60 | -1 -60 |
2 30 | -2 -30 |
3 20 | -3 -20 |
4 15 | -4 -15 |
5 12 | -5 -12 |
6 10 | -6 -10 |
Step 4: Find out which pair sums up to $\color{blue}{ b = -19 }$
PRODUCT = 60 and SUM = -19 | |
1 60 | -1 -60 |
2 30 | -2 -30 |
3 20 | -3 -20 |
4 15 | -4 -15 |
5 12 | -5 -12 |
6 10 | -6 -10 |
Step 5: Put -4 and -15 into placeholders to get factored form.
$$ \begin{aligned} x^{2}-19x+60 & = (x + \color{orangered}{\square} )(x + \color{orangered}{\square}) \\ x^{2}-19x+60 & = (x -4)(x -15) \end{aligned} $$