FOIL rule

The FOIL rule, also sometimes known as the double distributive property, is commonly taught to students learning algebra as a mnemonic (memory device) to remember how to multiply two binomials (polynomial with two terms). The name comes from the order of multiplying terms of the binomials as:

• (F)irst (first terms of each binomial are multiplied together)
• (O)uter ("outer" terms multiplied together)
• (I)nner ("inner" terms multiplied)
• (L)ast ("last" terms multiplied)

The answer is then the sum of the terms obtained from the method.

Example: (X+5)(X+5)

Answer:X²+10x+25

It is commonly taught, but is often frowned upon because the method does not work for higher order polynomials, and thus instead of actually teaching a general method, it is an example of learning by rules instead of concepts.