What is one factor of 2x^2-32y^2

Here you have two terms connected by the "subtraction" symbol.

The two coefficients are 2 and 32, and one factor common to both of these is 2. Thus, 2x^2-32y^2 = 2 (x^2-16y^2).

You could stop here. But it'd make more sense to continue, since x^2-16y^2 is easy to factor:

The three factors of 2x^2-32y^2 are 2, x-4 and x+4