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In mathematics, −1 is the additive inverse of 1, that is, the number that when added to 1 gives the additive identity element, 0. It is the negative integer greater than negative two (−2) and less than 0. Negative one bears relation to Euler's identity since In software development, −1 is a common initial value for integers and is also used to show that a variable contains no useful information. Negative one has some similar but slightly different properties to positive one.〔(Mathematical analysis and applications ) By Jayant V. Deshpande, ISBN 1-84265-189-7〕 ==Algebraic properties== Multiplying a number by −1 is equivalent to changing the sign on the number. This can be proved using the distributive law and the axiom that 1 is the multiplicative identity: for x real, we have : where we used the fact that any real x times 0 equals 0, implied by cancellation from the equation : In other words, : so (−1) · ''x'' is the arithmetic inverse of ''x'', or −''x''. 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「−1」の詳細全文を読む スポンサード リンク
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