Scalar Triple Product

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The scalar triple product of three vectors A, B, and C is denoted [A,B,C] and defined by

[A,B,C]=A·(BxC)
(1)
=B·(CxA)
(2)
=C·(AxB)
(3)
=det(ABC)
(4)
=|A_1 A_2 A_3; B_1 B_2 B_3; C_1 C_2 C_3|
(5)

where A·B denotes a dot product, AxB denotes a cross product, det(A)=|A| denotes a determinant, and A_i, B_i, and C_i are components of the vectors A, B, and C, respectively. The scalar triple product is a pseudoscalar (i.e., it reverses sign under inversion). The scalar triple product can also be written in terms of the permutation symbol epsilon_(ijk) as

 A·(BxC)=epsilon_(ijk)A^iB^jC^k,
(6)

where Einstein summation has been used to sum over repeated indices.

Additional identities involving the scalar triple product are

A·(BxC)=B·(CxA)=C·(AxB)
(7)
[A,B,C]D=[D,B,C]A+[A,D,C]B+[A,B,D]C
(8)
[q,q^',q^('')][r,r^',r^('')]=|q·r q·r^' q·r^(''); q^'·r q^'·r^' q^'·r^(''); q^('')·r q^('')·r^' q^('')·r^('')|.
(9)

The volume of a parallelepiped whose sides are given by the vectors A, B, and C is given by the absolute value of the scalar triple product

 V_(parallelepiped)=|A·(BxC)|.
(10)

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