FOIL is a mnemonic rule for multiplying binomial (that is, two-term) algebraic expressions.
FOIL abbreviates the sequence "First, Outside, Inside, Last"; it's a way of remembering that the product is the sum of the products of those four combinations of terms.

For instance, if we multiply the two expressions
(x + 1) (x + 2)
then the result is the sum of these four products:
x times x (the First terms of each expression)
x times 2 (the Outside pair of terms)
1 times x (the Inside pair of terms)
1 times 2 (the Last terms of each expression)
and so
(x + 1) (x + 2) = x^2 + 2x + 1x + 2 = x^2 + 3x + 2
[where the ^ is the usual way we indicate exponents here in Answers, because they're hard to represent in an online text environment].

Now, compare this to multiplying a pair of two-digit integers:
37 × 43
= (30 × 40) + (30 × 3) + (7 × 40) + (7 × 3)
= 1200 + 90 + 280 + 21
= 1591

The reason the two processes resemble each other is that multiplication is multiplication; the difference in the ways we represent the factors doesn't make it a fundamentally different operation.

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3 years ago