# FOIL Method

###### This wiki is incomplete.

PS: Here are examples of great wiki pages — Fractions, Chain Rule, and Vieta Root Jumping

#### Contents

## Information of FOIL

FOIL is a mnemonic for the standard method of multiplying two binomials. It's a handy way to remember how to multiply two binomials. This method is referred to as a FOIL method and is commonly used in linear binomials. FOIL is the acronym of "first, outside, inside, last."

- First: multiply the first terms in each set of parentheses.
- Outside: multiply the two terms on the outside.
- Inside/Inner: multiply both of the inside terms.
- Last: multiply the last terms in each set of parentheses.

For \(( 2x -5) (x -4),\) we have

- first: \(2x \times x=2x^2\)
- outside: \(2x \times (−4)= −8x\)
- inside: \(−5 \times x= −5x\)
- last: \((−5) \times (−4)= 20.\)

For \(( x + 3 ) ( x + 5 ),\) FOIL gives

\[\begin{align} ( x + 3 ) ( x + 5 ) &= x \cdot x + x \cdot 5 + 3 \cdot x + 3 \cdot 5\\ &= x^2 + 5x + 3x + 15\\ &=x^2 + 8x + 15. \end{align}\]

For \((2x + 3) (x - 5),\) FOIL gives the following:

- First: multiply \(2x\) with \(x\) to get \(2x^2.\)
- Outside: multiply \(2x\) with \(-5\) to get \(-10x.\)
- Inside: multiply \(3\) with \(x\) to get \(3x.\)
- Last: multiply \(3\) with \(-5\) to get \(-15.\)
Therefore, \((2x + 3) (x - 5) = 2x^2-7x-15.\)

## Reverse FOIL

The FOIL rule converts a product of two binomials into a sum of four monomials/power products. This reverse process is called factorization.