Step 1: 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:
$$ \color{blue}{ b = -8 } ~ \text{ and } ~ \color{red}{ c = -768 }$$Now we must discover two numbers that sum up to $ \color{blue}{ -8 } $ and multiply to $ \color{red}{ -768 } $.
Step 2: Find out pairs of numbers with a product of $\color{red}{ c = -768 }$.
PRODUCT = -768 | |
-1 768 | 1 -768 |
-2 384 | 2 -384 |
-3 256 | 3 -256 |
-4 192 | 4 -192 |
-6 128 | 6 -128 |
-8 96 | 8 -96 |
-12 64 | 12 -64 |
-16 48 | 16 -48 |
-24 32 | 24 -32 |
Step 3: Find out which pair sums up to $\color{blue}{ b = -8 }$
PRODUCT = -768 and SUM = -8 | |
-1 768 | 1 -768 |
-2 384 | 2 -384 |
-3 256 | 3 -256 |
-4 192 | 4 -192 |
-6 128 | 6 -128 |
-8 96 | 8 -96 |
-12 64 | 12 -64 |
-16 48 | 16 -48 |
-24 32 | 24 -32 |
Step 4: Put 24 and -32 into placeholders to get factored form.
$$ \begin{aligned} x^{2}-8x-768 & = (x + \color{orangered}{\square} )(x + \color{orangered}{\square}) \\ x^{2}-8x-768 & = (x + 24)(x -32) \end{aligned} $$