Step 1 :
After factoring out $ 12 $ we have:
$$ 12x^{2}-276x+1080 = 12 ( x^{2}-23x+90 ) $$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:
$$ \color{blue}{ b = -23 } ~ \text{ and } ~ \color{red}{ c = 90 }$$Now we must discover two numbers that sum up to $ \color{blue}{ -23 } $ and multiply to $ \color{red}{ 90 } $.
Step 3: Find out pairs of numbers with a product of $\color{red}{ c = 90 }$.
PRODUCT = 90 | |
1 90 | -1 -90 |
2 45 | -2 -45 |
3 30 | -3 -30 |
5 18 | -5 -18 |
6 15 | -6 -15 |
9 10 | -9 -10 |
Step 4: Find out which pair sums up to $\color{blue}{ b = -23 }$
PRODUCT = 90 and SUM = -23 | |
1 90 | -1 -90 |
2 45 | -2 -45 |
3 30 | -3 -30 |
5 18 | -5 -18 |
6 15 | -6 -15 |
9 10 | -9 -10 |
Step 5: Put -5 and -18 into placeholders to get factored form.
$$ \begin{aligned} x^{2}-23x+90 & = (x + \color{orangered}{\square} )(x + \color{orangered}{\square}) \\ x^{2}-23x+90 & = (x -5)(x -18) \end{aligned} $$