Step 1 :
After factoring out $ 3w $ we have:
$$ 3w^{3}+12w^{2}-135w = 3w ( w^{2}+4w-45 ) $$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:
$$ \color{blue}{ b = 4 } ~ \text{ and } ~ \color{red}{ c = -45 }$$Now we must discover two numbers that sum up to $ \color{blue}{ 4 } $ and multiply to $ \color{red}{ -45 } $.
Step 3: Find out pairs of numbers with a product of $\color{red}{ c = -45 }$.
PRODUCT = -45 | |
-1 45 | 1 -45 |
-3 15 | 3 -15 |
-5 9 | 5 -9 |
Step 4: Find out which pair sums up to $\color{blue}{ b = 4 }$
PRODUCT = -45 and SUM = 4 | |
-1 45 | 1 -45 |
-3 15 | 3 -15 |
-5 9 | 5 -9 |
Step 5: Put -5 and 9 into placeholders to get factored form.
$$ \begin{aligned} w^{2}+4w-45 & = (x + \color{orangered}{\square} )(x + \color{orangered}{\square}) \\ w^{2}+4w-45 & = (x -5)(x + 9) \end{aligned} $$