Lagrange's identity is the algebraic identity

(Mitrinovic 1970, p. 41). In determinant form,

where
is the determinant of
. Lagrange's identity is a special case of the Binet-Cauchy identity, and Cauchy's inequality in n dimensions follows from it. It can be coded in Mathematica as follow.
Plugging in gives the n = 2 and n = 3 identities




(1)
(Mitrinovic 1970, p. 41). In determinant form,

(2)
where


Plugging in gives the n = 2 and n = 3 identities

(3)


(4)
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