Explanation

The formula 4ab can be factored as:

4ab = (a + b)^2 - (a - b)^2

This is a difference of squares identity, where (a + b)^2 expands to a^2 + 2ab + b^2, and (a - b)^2 expands to a^2 - 2ab + b^2.

Subtracting these two expressions eliminates the a^2 and b^2 terms, leaving 4ab.