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In elementary algebra, ''FOIL'' is a mnemonic for the standard method of multiplying two binomials—hence the method may be referred to as the FOIL method. The word ''FOIL'' is an acronym for the four terms of the product: * First ("first" terms of each binomial are multiplied together) * Outer ("outside" terms are multiplied—that is, the first term of the first binomial and the second term of the second) * Inner ("inside" terms are multiplied—second term of the first binomial and first term of the second) * Last ("last" terms of each binomial are multiplied) The general form is: : Note that is both a "first" term and an "outer" term; is both a "last" and "inner" term, and so forth. The order of the four terms in the sum is not important, and need not match the order of the letters in the word FOIL. ==History== The FOIL method is a special case of a more general method for multiplying algebraic expressions using the distributive law. The word ''FOIL'' was originally intended solely as a mnemonic for high-school students learning algebra. The term appears in William Betz's 1929 text, ''Algebra for Today'', where he states: ... first terms, outer terms, inner terms, last terms. (The rule stated above may also be remembered by the word FOIL, suggested by the first letters of the words first, outer, inner, last.) William Betz was active in the mathematics reform movement in the United States at that time, had written many texts on elementary mathematics topics and had "devoted his life to the improvement of mathematics education." Many students and educators in the United States now use the word "foil" as a verb meaning "to expand the product of two binomials". This neologism has not gained widespread acceptance in the mathematical community. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「FOIL method」の詳細全文を読む スポンサード リンク
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