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In algebra, the Binet–Cauchy identity, named after Jacques Philippe Marie Binet and Augustin-Louis Cauchy, states that 〔 〕 : for every choice of real or complex numbers (or more generally, elements of a commutative ring). Setting ''ai'' = ''ci'' and ''bj'' = ''dj'', it gives the Lagrange's identity, which is a stronger version of the Cauchy–Schwarz inequality for the Euclidean space . ==The Binet–Cauchy identity and exterior algebra== When ''n'' = 3 the first and second terms on the right hand side become the squared magnitudes of dot and cross products respectively; in ''n'' dimensions these become the magnitudes of the dot and wedge products. We may write it : where a, b, c, and d are vectors. It may also be written as a formula giving the dot product of two wedge products, as : In the special case of unit vectors ''a=c'' and ''b=d'', the formula yields : When both vectors are unit vectors, we obtain the usual relation : where φ is the angle between the vectors. 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「Binet–Cauchy identity」の詳細全文を読む スポンサード リンク
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