Step 1 :

After factoring out $ 7x $ we have:

$$ 7x^{3}+21x^{2}-63x = 7x ( x^{2}+3x-9 ) $$

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:

$$ \color{blue}{ b = 3 } ~ \text{ and } ~ \color{red}{ c = -9 }$$

Now we must discover two numbers that sum up to $ \color{blue}{ 3 } $ and multiply to $ \color{red}{ -9 } $.

Step 3: Find out pairs of numbers with a product of $\color{red}{ c = -9 }$.

PRODUCT = -9
-1     9	1     -9
-3     3	3     -3

Step 4: Because none of these pairs will give us a sum of $ \color{blue}{ 3 }$, we conclude the polynomial cannot be factored.

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