Step 1 :
After factoring out $ 4 $ we have:
$$ 4x^{2}-20x-96 = 4 ( x^{2}-5x-24 ) $$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:
$$ \color{blue}{ b = -5 } ~ \text{ and } ~ \color{red}{ c = -24 }$$Now we must discover two numbers that sum up to $ \color{blue}{ -5 } $ and multiply to $ \color{red}{ -24 } $.
Step 3: Find out pairs of numbers with a product of $\color{red}{ c = -24 }$.
PRODUCT = -24 | |
-1 24 | 1 -24 |
-2 12 | 2 -12 |
-3 8 | 3 -8 |
-4 6 | 4 -6 |
Step 4: Find out which pair sums up to $\color{blue}{ b = -5 }$
PRODUCT = -24 and SUM = -5 | |
-1 24 | 1 -24 |
-2 12 | 2 -12 |
-3 8 | 3 -8 |
-4 6 | 4 -6 |
Step 5: Put 3 and -8 into placeholders to get factored form.
$$ \begin{aligned} x^{2}-5x-24 & = (x + \color{orangered}{\square} )(x + \color{orangered}{\square}) \\ x^{2}-5x-24 & = (x + 3)(x -8) \end{aligned} $$