Consider two rectangular Cartesian coordinate systems that are translated and rotated with respect to each other. The transformation between the two coordinate systems is given by
x̄ = c + Lx
where c is a vector and L = [lij] is the matrix of directional cosines, lij ≡ êi · êj
Deduce that the following orthogonality conditions hold:
L · LT = I or liklkj = δij.
That is, L is an orthogonal matrix.