Answer:
We can describe FOIL using the distributive property of multiplication. For real numbers x, y, and z the distributive property of multiplication states that

Now let
, where v and w are real numbers.
Then 
Here, we can again use the distributive property of multiplication to get

Hence, it follows that

This is the method of FOIL (first: xv, outside: xw, inside: yv, last: yw)
For example, 