How would the expression x^2-4 be rewritten using difference of squares?

a2 – b2 = (a + b)(a – b) or (a – b)(a + b).
This is the 'Difference of Squares' formula we can use to factor the expression.

In order to use the 'Difference of Squares' formula to factor a binomial, the binomial must contain two perfect squares that are separated by a subtraction symbol.

x^2 - 4 fits this, because x^2 and 4 are both perfect squares, and they are separated by a subtraction symbol.
All you do here to factor, is take the square root of each term.

√x^2 = x
√4 = 2

Now that we have our square roots, x and 2, we substitute these numbers into the form (a + b)(a - b).

(a + b)(a - b)
(x + 2)(x - 2)

Our answer is final (x + 2)(x - 2), which can also be written as (x - 2)(x + 2), it doesn't make a difference which order you put it in.

Anyway, Hope this helps!!
Let me know if you need help understanding anything and I'll try to explain as best I can.