To find the Greatest Common Factor (GCF) of the given expression, we need to factor it completely.
The given expression is 20x^2 - 420x - 420x - 4.
First, let's see if there are any common factors among the terms. We can see that both terms have a common factor of 4, so let's factor it out:
4(5x^2 - 105x - 105x - 1)
Now, let's focus on factoring the trinomial within the parentheses: 5x^2 - 105x - 105x - 1.
This trinomial can be factored as:
5x(x - 21) - 1(7x + 1)
So, the fully factored form of the expression is:
4[5x(x - 21) - 1(7x + 1)]
Now, we can see that there are no other common factors that can be factored out from all the terms.
The GCF is the product of the common factors raised to the lowest exponent. In this case, the common factor is 4.
Therefore, the GCF of the expression 20x^2 - 420x - 420x - 4 is 4.