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:
$$ \color{blue}{ b = 3 } ~ \text{ and } ~ \color{red}{ c = -70 }$$Now we must discover two numbers that sum up to $ \color{blue}{ 3 } $ and multiply to $ \color{red}{ -70 } $.
Step 2: Find out pairs of numbers with a product of $\color{red}{ c = -70 }$.
PRODUCT = -70 | |
-1 70 | 1 -70 |
-2 35 | 2 -35 |
-5 14 | 5 -14 |
-7 10 | 7 -10 |
Step 3: Find out which pair sums up to $\color{blue}{ b = 3 }$
PRODUCT = -70 and SUM = 3 | |
-1 70 | 1 -70 |
-2 35 | 2 -35 |
-5 14 | 5 -14 |
-7 10 | 7 -10 |
Step 4: Put -7 and 10 into placeholders to get factored form.
$$ \begin{aligned} x^{2}+3x-70 & = (x + \color{orangered}{\square} )(x + \color{orangered}{\square}) \\ x^{2}+3x-70 & = (x -7)(x + 10) \end{aligned} $$