Step 1 :
After factoring out $ 3x $ we have:
$$ 3x^{3}-18x^{2}+24x = 3x ( x^{2}-6x+8 ) $$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:
$$ \color{blue}{ b = -6 } ~ \text{ and } ~ \color{red}{ c = 8 }$$Now we must discover two numbers that sum up to $ \color{blue}{ -6 } $ and multiply to $ \color{red}{ 8 } $.
Step 3: Find out pairs of numbers with a product of $\color{red}{ c = 8 }$.
PRODUCT = 8 | |
1 8 | -1 -8 |
2 4 | -2 -4 |
Step 4: Find out which pair sums up to $\color{blue}{ b = -6 }$
PRODUCT = 8 and SUM = -6 | |
1 8 | -1 -8 |
2 4 | -2 -4 |
Step 5: Put -2 and -4 into placeholders to get factored form.
$$ \begin{aligned} x^{2}-6x+8 & = (x + \color{orangered}{\square} )(x + \color{orangered}{\square}) \\ x^{2}-6x+8 & = (x -2)(x -4) \end{aligned} $$