The algebraic identity


Letting
and
gives Lagrange's identity.
The n = 2 case gives


The n = 3 case is equivalent to the vector identity

where
is the dot product and
is the cross product. Note that this identity itself is sometimes known as Lagrange's identity.


(1)
Letting


The n = 2 case gives


(2)
The n = 3 case is equivalent to the vector identity

(3)
where


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